Prof. Dr. Maihe Li

Alpine treelines ecotones are critical ecological transition zones and are highly sensitive to global warming. However, the impact of climate on the distribution of treeline trees is not yet fully understood as this distribution may also be affected by other factors. Here, we used high-resolution satellite images with climatic and topographic variables to study changes in treeline tree distribution in the alpine treeline ecotone of the Changbai Mountain for the years 2002, 2010, 2017, and 2021. This study employed the Geodetector method to analyze how interactions between climatic and topographic factors influence the expansion of Betula ermanii on different aspect slopes. Over the past 20 years, B. ermanii, the only tree species in the Changbai Mountain tundra zone, had its highest expansion rate from 2017 to 2021 across all the years studied, approaching 2.38% per year. In 2021, B. ermanii reached its uppermost elevations of 2224 m on the western aspects and 2223 m on the northern aspects, which are the predominant aspects it occupies. We also observed a notable increase in the distribution of B. ermanii on steeper slopes (> 15°) between 2002 and 2021. Moreover, we found that interactions between climate and topographic factors played a more significant role in B. ermanii's expansion than any single dominant factor. Our results suggest that the interaction between topographic wetness index and the coldest month precipitation (Pre₁), contributing 91% of the observed variability, primarily drove the expansion on the southern aspect by maintaining soil moisture, providing snowpack thermal insulation which enhanced soil temperatures, decomposition, and nutrient release in harsh conditions. On the northern aspect, the interaction between elevation and mean temperature of the warmest month explained 80% of the expansion. Meanwhile, the interaction between Pre₁ and mean temperature of the growing season explained 73% of the expansion on the western aspect. This study revealed that dominant factors driving treeline upward movement vary across different mountain aspects. Climate and topography play significant roles in determining tree distribution in the alpine treeline ecotone. This knowledge helps better understand and forecast treeline dynamics in response to global climate change.

Carbon (C) allocation among different plant tissues is crucial for maintaining C balance in forest ecosystems, especially under changing climate conditions. The partitioning of newly assimilated C among plant tissues, interconnected ramets and soil in forests dominated by giant clonal plants, such as moso bamboo (Phyllostachys edulis), and the influence of drought on this partitioning remain poorly understood.
In August 2019, we performed in situ labelling of the entire crown of R0 (ramets that emerged in 2019) of moso bamboo with ¹³CO₂ in plots subjected to a 5-year drought or left untreated (ambient control) in subtropical China. We then traced the ¹³C signatures in the leaves, twigs and fine roots of R0, R1 (ramets that emerged in 2018 and are connected with R0) and R2 (ramets that emerged in 2017 and are connected with R1), as well as in soil organic C (SOC) and soil respiration over the course of 1-year post-labelling.
Drought reduced leaf ¹³C assimilation and its allocation to sink tissues but did not alter the velocity of C transport from source to sink compared to controls. The peak ¹³C signal was observed on day 15 for SOC and on day 5 for respired CO₂ in both drought and ambient control forests. Labelled ¹³C was detected in R1 ramets on day 3 and in R2 on day 7 post-labelling. This study reveals that new assimilates produced by the ‘younger’ R0 ramets are preferentially retained within their own tissues to meet their own demands rather than being allocated to interconnected neighbouring R1 and R2 ramets.
Synthesis. In forests dominated by large clonal plants, such as giant moso bamboo, drought can alter the allocation of newly assimilated C within the tissues of source ramets but may not affect its allocation among interconnected ramets or within plant–soil systems. Our findings highlight the complexity of newly assimilated C partitioning in these forests and suggest that clonal integration may mitigate drought-induced dieback in older ramets through resource sharing under climate change.

Soil microbes regulate nutrient cycling, organic matter decomposition, and other processes, thereby maintaining soil multifunctionality (SMF). However, the relationship between microbial characteristics and soil multifunctionality has primarily been studied in bulk soils, with less attention to rhizosphere soils. Moreover, this relationship remains unclear within a single forest type across large scales. In this study, we selected six sites across the distribution range of moso bamboo (Phyllostachys edulis (Carrière) J. Houz.) in China to quantify the relationship between microbial communities and soil multifunctionality in both rhizosphere and bulk soil, and to evaluate how abiotic factors influence this relationship. Our results showed that microbial diversity was negatively correlated with SMF, while the key microbial drivers (bacteria or fungi) of SMF varied between soil compartments (i.e., rhizosphere and bulk soil). Soil variables influenced SMF in bulk soils by affecting bacterial diversity and fungal composition, whereas in rhizosphere soils, soil variables influenced SMF primarily by affecting fungal diversity and composition, suggesting that different characteristics of bacterial and fungal communities drive SMF. Climatic factors exert a more significant influence on the multifunctionality of rhizosphere soils compared to bulk soils. Considering the intricate interplay between plants and soil microbes, our study highlights the importance of integrating SMF and microbial community structure within distinct soil compartments.

Background and aims The biogeochemical niche framework, which estimates plant species niches based on their elemental composition (elementome), offers valuable insights into plant nutritional strategies, community assembly, and elemental cycling within ecosystems. Although the biogeochemical niche hypothesis has been validated in various terrestrial ecosystems, its application in transitional zones between contrasting biomes, such as in Eurasian forest-steppe ecotones, remains underexplored.
Methods This study investigates the biogeochemical niche framework in seven sites along a gradient from closed-canopy forests to forest-steppe ecotones and meadow steppes in northeastern China, which constituents a critical component of the Eurasian biome. We analyzed the concentrations of ten essential elements—both macro- and micro-elements—in leaves of the dominant plant species, and assessed the elemental compositions and physicochemical properties of the soil at each site.
Results We found substantial differences in leaf elementomes among species across the three habitats, primarily attributed to phylogenetic legacy and species taxonomy. Woody plants in the ecotone exhibited higher leaf elemental homeostasis compared to herbaceous plants; the latter displayed notable elemental plasticity.
Conclusions Results from this study highlight the applicability of leaf elementome as a universal metric for comparing species niches across different life forms. Moreover, our findings offer empirical support for the biogeochemical niche conservatism assumption, suggesting that species-specific elemental utilization is a critical niche differentiation process in driving species coexistence within Eurasian forest-steppe ecotones.

Background: Phosphorus (P) availability in soils regulates forest productivity. However, the drivers of soil P dynamics following forest management remain poorly understood, particularly in P-deficient forests in tropical and subtropical regions.
Method: Soil samples of 0–10 cm were collected from the plots after 9 years of thinning and understory removal (UR) in Pinus massoniana plantations in subtropical China. Soil physicochemical properties, microbial biomass and community composition, and Hedley P fractions were measured to assess the underlying mechanisms for the dynamics of soil P fractions.
Results: Compared to undisturbed plots, total soil inorganic P (Pi; + 24%) within the dominant species thinning (DST) plots showed a significant increase, which was associated with the accrual in resin-Pi (+ 30%), NaHCO₃-Pi (+ 21%), and C.CHl-Pi (+ 45%). These Pi fractions were primarily correlated with increased relative abundance of Ascomycota, Rozellomycota, and Proteobacteria. Conversely, post-management (thinning and UR) assessments revealed no significant changes in total P, total organic P (Po), and residual P. The observed decrease in total Po (– 9%) in DST plots was linked to reductions in NaHO-Po (– 7%) and C.CHl-Po (– 24%). Notably, these Po fractions were negatively affected by the relative abundance of Glomeromycota. Furthermore, variations in soil fungal and bacterial community structures accounted for 44.3% and 26.3% of the variances in soil Pi fractions, respectively, similarly explaining 20.4% and 33.3% for soil Po fractions, respectively.
Conclusions: These results indicate that P availability following forest management interventions within subtropical pine plantations is intricately connected to microbial community composition that enhances the transformation from Po into Pi forms.

1. Although neighbourhood interactions are important for the establishment and survival of tree line trees, it remains poorly understood how they affect growth rates under changing climatic conditions.
2. Here, we combine census data and dendrochronological measurements from 18 tree line plots between 4300 and 4520 m asl on the eastern Tibetan Plateau to develop a retrospective Neighbourhood Index. We then investigate whether tree interaction is facilitative or competitive and whether it changes over time.
3. Our results show that competition for water not only dominates neighbourhood interactions on the eastern Tibetan Plateau, but also increased significantly from 1960 to 2009 (p < 0.001).
4. Contrary to the common belief of facilitative neighbourhood interactions at high elevation, we demonstrate that competition among mature trees is common in tree line ecotones of the eastern Tibetan Plateau, and likely to increase under projected global warming.

Anthropogenic nitrogen (N) inputs can significantly impact nutrient cycling and ecosystem functioning in terrestrial ecosystems. However, the effects of N addition on phosphorus (P) cycling processes in forest ecosystems remain unclear. In this study, we combined data from a long-term (11-year) N addition experiment across seven different forests ranging from temperate to tropical biomes, with a global meta-analysis from 88 relevant publications, to investigate the responses of P cycling-related variables to N inputs in forest ecosystems. We found that N addition had little effect on most P cycling-related variables (e.g., leaf P, soil total P, soil available P, soil P fractions, and microbial biomass P) across the studied forest ecosystems. The meta-analysis highlighted that N-induced changes in P cycling were highly variable. Only a few variables, such as the leaf P concentration and the activity of soil acid phosphatase, presented significant responses to N addition and changed with climatic zone and the amount and duration of N inputs. Our study suggests that P cycling processes in forest ecosystems remain largely unaffected by N inputs. Our findings contribute to a better understanding and prediction of biogeochemical cycles in the context of N deposition related to anthropogenic activities and global climate change.

Alpine treeline ecotones are highly sensitive to climate warming. The low temperature-determined alpine treeline is expected to shift upwards in response to global warming. However, little is known about how temperature interacts with other important factors to influence the distribution range of tree species within and beyond the alpine treeline ecotone. Hence, we used a GF-2 satellite image, along with bioclimatic and topographic variables, to develop an ensemble suitable habitat model based on the species distribution modeling algorithms in Biomod2. We investigated the distribution of suitable habitats for B. ermanii under three climate change scenarios (i.e., low (SSP126), moderate (SSP370) and extreme (SSP585) future emission trajectories) between two consecutive time periods (i.e., current–2055, and 2055–2085). By 2055, the potential distribution range of B. ermanii will expand under all three climate scenarios. The medium and high suitable areas will decline under SSP370 and SSP585 scenarios from 2055 to 2085. Moreover, under the three climate scenarios, the uppermost altitudes of low suitable habitat will rise to 2329 m a.s.l., while the altitudes of medium and high suitable habitats will fall to 2201 and 2051 m a.s.l. by 2085, respectively. Warming promotes the expansion of B. ermanii distribution range on the Changbai Mountain, and this expansion will be modified by precipitation as climate warming continues. This interaction between temperature and precipitation plays a significant role in shaping the potential distribution range of B. ermanii in the alpine treeline ecotone. This study reveals the link between environmental factors, habitat distribution, and species distribution in the alpine treeline ecotone, providing valuable insights into the impacts of climate change on high-elevation vegetation, and contributing to mountain biodiversity conservation and sustainable development.

Background: Soil erosion affects the stability of terrestrial ecosystems and ecosystem services by directly or indirectly impacting the cycling of soil materials and energy and reducing the fertility of grassland soils. However, research on microbial adaptation to grazing and soil erosion is limited, particularly in relation to grassland ecosystem restoration. Here, we assess microbial communities subjected to simulated soil erosion and grazing in a semi-arid grassland of Inner Mongolia, China.

Results: No significant change was observed in soil variables. However, the structure of the soil microbial community underwent significant changes as a result of soil erosion and soil erosion plus grazing, leading to a significant increase in the relative abundance of Cyanobacteria (116.80% vs 116.38%). Wind erosion and deposition contributed to an increase in the network complexity of soil bacterial and fungal communities. However, much of this effect was alleviated by grazing. Simultaneously, aeolian processes and grazing regulate soil microbial community assembly, leading to inconsistent patterns of change in bacterial and fungal communities. Under wind erosion and deposition, the relative contribution of deterministic processes (4.44% vs 31.11%) in bacterial communities increased, while the relative contribution of stochastic processes (2.23% vs 20%) in fungal communities reduced. Grazing resulted in a decrease in the relative contribution of deterministic processes (8.89%) in the bacterial community and an increase in the relative contribution of stochastic processes (8.89%) in the fungal community.

Conclusion: This study presents a comprehensive investigation of the response of soil microbial communities to aeolian erosion–deposition and grazing in a semi-arid grassland. Our findings indicate that microbial communities in the semi-arid grassland show resistance to external disturbances and that light grazing mitigates the effects of aeolian erosion–deposition on microbial communities, which is essential for maintaining the stability and biodiversity of grassland ecosystems.

Understanding the physiological adaptations of non-treeline trees to environmental stress is important to understand future shifts in species composition and distribution of current treeline ecotone. The aim of the present study was to elucidate the mechanisms of the formation of the upper elevation limit of non-treeline tree species, Picea jezoensis, and the carbon allocation strategies of the species on Changbai Mountain. We employed the ¹³C in situ pulse labeling technique to trace the distribution of photosynthetically assimilated carbon in Picea jezoensis at different elevational positions (tree species at its upper elevation limit (TSAUE, 1700 m a.s.l.) under treeline ecotone; tree species at a lower elevation position (TSALE, 1400 m a.s.l.). We analyzed ¹³C and the non-structural carbohydrate (NSC) concentrations in various tissues following labeling. Our findings revealed a significant shift in carbon allocation in TSAUE compared to TSALE. There was a pronounced increase in δ¹³C allocation to belowground components (roots, soil, soil respiration) in TSAUE compared to TSALE. Furthermore, the C flow rate within the plant-soil-atmosphere system was faster, and the C residence time in the plant was shorter in TSAUE. The trends indicate enhanced C sink activity in belowground tissues in TSAUE, with newly assimilated C being preferentially directed there, suggesting a more conservative C allocation strategy by P. jezoensis at higher elevations under harsher environments. Such a strategy, prioritizing C storage in roots, likely aids in withstanding winter cold stress at the expense of aboveground growth during the growing season, leading to reduced growth of TSAUE compared to TSALE. The results of the present study shed light on the adaptive mechanisms governing the upper elevation limits of non-treeline trees, and enhances our understanding of how non-treeline species might respond to ongoing climate change.

Drought stress caused by global climate warming affects tree growth in both dry and wet areas. However, the differences in tree growth responses to drought in dry and wet areas are poorly understood. Here, we collected 93 tree cores to analyze the differences in the radial growth responses of larch (Larix gmelinii) under climate change and tree growth resilience under drought events in the Altai Mountains (dry area) and Changbai Mountains (wet area). The results showed that larch growth in the Altai Mountains was significantly positively correlated with the self-calibrating Palmer Drought Severity Index (sc-PDSI) in all months and precipitation in the previous growth season and May, whereas it was significantly (p < 0.05) negatively correlated with temperature in May and the previous June to August. In the Changbai Mountains, larch growth was significantly positively correlated with May maximum and mean temperature, and significantly positively and negatively correlated with precipitation in April and May，respectively (p < 0.05). The mean resistance (recovery) of larch growth to drought in wet areas were significantly stronger (weaker) than that in dry areas (p < 0.05). Moreover, strengthening the drought frequency led to a significant (p < 0.05) decline in larch resistance in dry areas. Therefore, warming-induced increases in drought stress will aggravate negative impacts on the radial growth of larch forests in temperate dry areas but not in wet areas in the future.

Soil stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) are indicators for nutrient balance. Shrub encroachment into grasslands could change nutrient concentrations and stoichiometry in soils, but the general patterns remain unclear. With a meta-analysis of a global dataset covering 344 observations from 68 studies, we examined the responses of grassland soil C:N:P stoichiometry to shrub encroachment under various environmental conditions. Our results show that: 1) Shrub encroachment significantly increased the concentrations of soil C (+29 %), N (+25 %), P (+20 %), C:N (+5 %), C:P (+12 %), and N:P (+6 %). The magnitude of such effects varied with climate, soil texture, and soil layer. 2) Increases in SOC and TN concentrations mainly occurred in Mediterranean and very humid climate zones. Soil C:P and N:P decreased in semi-humid climate zone after shrub encroachment. 3) The increases in SOC and TN concentrations and in the C:N, C:P, and N:P ratios after shrub encroachment were greater in the topsoil than in deeper soil layers. 4) Both finest-textured soil (clay) and coarsest-textured soil (sand) are beneficial for increase of soil nutrient concentrations following shrub encroachment. 5) The magnitude of the change in soil C:N was negatively correlated with the duration of shrub encroachment, due to greater increases in soil TN than in SOC concentrations with longer durations of encroachment. Our results indicate that soil stoichiometric shifts in shrub-encroached grasslands are relatively sensitive to environmental factors, including soil texture, soil pH, and climate. These findings help us to better understand the effects of shrub encroachment on biogeochemical cycling, functioning, and services in grasslands across a broad range of spatio-temporal scales.

Introduction: The variety of organs carbon concentration may be important for tree survival rate, drought resistance and tree subsequent recovery. However, it remains unclear how drought affect structural carbohydrate (SC) and non–structural carbohydrate (NSC) export and transport on clonal plant, which can be correlated with sustain physiological metabolism and group drought resistance by resource sharing. To better understand the adaption ability of clone plants to drought and the linkage of organ carbon with soil organic carbon (SOC) fractions, we assessed how long–term drought affects organ carbon and its impact on SOC fractions among moso bamboo (Phyllostachys edulis) ramets.

Methods: Throughfall exclusion included two treatments with simulated drought (TE) and control sample (CK, natural rainfall) by waterproofing panels, which excluded 70–80% of the precipitation. We measured the SC and NSC of leaves, branches and roots as well as soil organic carbon components on three ramets, which emerged in 2017 (grandma, GB), ramets that appeared in 2018 (mother bamboo, MB) and ramets emerging in 2019 (current-year bamboo, CB).

Results: The results showed that there was significant difference on lignin, cellulose: lignin ratio and soluble sugar in leaves and roots (p<0.05) instead of branches (p>0.05). Effect of drought on SC and NSC varied with different organs and ramet age. Drought significantly increased soluble sugar concentration of leaves and roots by 15.5–31.0% and 10.6–24.8% for current-year bamboo. Compared with CK, drought decreased SOC by 6.7–19.1%, microbial biomass carbon (MBC) by 55.3–68.7%, readily oxidizable carbon (ROC) by 11.2–29.8%, particulate organic carbon (POC) by 25.1–47.4% but no effect on mineral–associated organic carbon (MOC). Drought changed the relationships of carbon components between plant organs and soil. In the control treatments, SC of leaves were significantly positively correlated with ROC, NSC of branches were positively correlated with ROC and MBC, NSC of roots were significantly positively correlated with SOC.

Discussion: Overall, our results suggest that drought strengthened the linkage of plant organ carbon and soil carbon cycling among moso bamboo ramets in ecosystem studies, which are critical for predicting tree resistance and management in subtropical forest under drought.

The importance of fine-root diameter for ecosystem functioning is increasingly recognized, yet much remains to be learned about the variation in fine-root diameter at large scales. We conducted an analysis of fine-root diameter for five root orders for 1163 plant species to detect patterns in relation to resource availability (e.g. carbon, nitrogen, water and net primary production (NPP)), stress intensity (e.g. plant/soil biodiversity and soil bulk density) and temperature. First- to fourth-order root diameters showed non-linear relationships with mean annual temperature (except for first-order root diameter) and/or with latitude. The diameters of the five root orders decreased with increasing mean annual precipitation, but increased with greater NPP, which was the strongest determinant of fine-root diameter. Increasing soil biodiversity was associated with decreasing diameters of fourth- and fifth-order roots, while greater plant biodiversity was associated with decreasing diameters of first- to third-order roots. Soil total nitrogen concentration had a positive effect on first-order root diameter but a negative effect on fourth- and fifth-order root diameters. The patterns reversed for soil total phosphorus concentration. First- to third-order and fifth-order root diameters increased with greater soil bulk density. Second- to fourth-order root diameters increased with higher soil pH. Overall, the variables related to climatic, biological and edaphic factors explained 44–63% of the total variance in the diameters of the different root orders. The unique patterns of plasticity observed in fine-root diameter across root orders in response to varying environmental conditions contributes to a diversification of plant strategies for nutrient/water acquisition and transport under climate change.

Different fungal guilds within the soil fungal community regulate forest ecosystem processes. Soil fungi are dictated by edaphic factors such as soil water and nutrient availabilities. However, how the total number of fungi and the composition of different fungal guilds in the soil vary under covarying pattern of nitrogen deposition and precipitation regime in temperate forests has not been well documented. In this study, we explored the effects of long-term nitrogen-water interactions on the diversity and composition of soil overall fungi and different fungal guilds, and their relationships with fine-root and soil fungal mycelial traits in a temperate forest. The diversity of the totality of soil fungi or any fungal guilds did not change, but the community composition of saprotrophic and symbiotrophic fungi was significantly changed by nitrogen addition (N), showing increased abundance of soil symbiotrophic fungi but decreased abundance of soil saprotrophic fungi. Precipitation reduction (W) significantly altered soil overall and pathotrophic fungal community. Precipitation reduction combined with nitrogen addition (WN) significantly changed soil overall, pathotrophic and symbiotrophic fungal community composition. Soil pathotrophic, saprotrophic and symbiotrophic fungal community composition was variously related to fine-root diameter, root tissue density, nitrogen and/or phosphorus concentration. Long-term nitrogen-water interactions decreased the complexity of soil fungal networks, reflected by the lower edges and average degree, but the higher average path distance and modularity. These findings of soil fungal guild-specific responses to nitrogen-water interactions will deepen our understanding of soil carbon sequestration potential and nutrient cycling in temperate forest ecosystems under future climate changes.

Both macronutrients and micronutrients are essential for tree growth and development through participating in various ecophysiological processes. However, the impact of the nutritional status of trees on their ability to withstand drought-induced mortality remains inconclusive. We thus conducted a comprehensive meta-analysis, compiling data on 11 essential nutrients from 44 publications (493 independent observations). Additionally, a field study was conducted on Pinus sylvestris L. trees with varying drought-induced vitality loss in the "Visp" forest in southern Switzerland. No consistent decline in tree nutritional status was observed during tree mortality. The meta-analysis revealed significantly lower leaf potassium (K), iron (Fe), and copper (Cu) concentrations with tree mortality. However, the field study showed no causal relationships between nutritional levels and the vitality status of trees. This discrepancy is mainly attributed to the intrinsic differences in the two types of experimental designs and the ontogenetic stages of target trees. Nutrient reductions preceding tree mortality were predominantly observed in non-field conditions, where the study was conducted on seedlings and saplings with underdeveloped root systems. It limits the nutrient uptake capacity of these young trees during drought. Furthermore, tree nutritional responses are also influenced by many variables. Specifically, (a) leaf nutrients are more susceptible to drought stress than other organs; (b) reduced tree nutrient concentrations are more prevalent in evergreen species during drought-induced mortality; (c) of all biomes, Mediterranean forests are most vulnerable to drought-induced nutrient deficiencies; (d) soil types affect the direction and extent of tree nutritional responses. We identified factors that influence the relationship between tree nutritional status and drought survival, and proposed potential early-warning indicators of impending tree mortality, for example, decreased K concentrations with declining vitality. These findings contribute to our understanding of tree responses to drought and provide practical implications for forest management strategies in the context of global change.

Volcanic lava is an excellent model of primary succession, in which basalt-associated microorganisms drive the cycling of different elements such as nitrogen, carbon, and other nutrients. Microbial communities in volcanic soils are of particular interest for study on the emergence and evolution of life within special and extreme conditions. The initial processes of colonization and subsequent rock weathering by microbial communities are still poorly understood. We analyzed the soil bacterial and fungal communities and diversities associated with lava (LBL) and kipuka (BK) sites in Wudalianchi using 16S and ITS rRNA Illumina Miseq sequencing techniques. The results showed that soil physical and chemical properties (pH, MC, TOC, TN, TP, AP, DOC, and DON) significantly differed between LBL and BK. The Shannon, Ace, and Pd indexes of fungi in the two sites showed a significant difference (p < 0.05). The dominant bacterial phyla forming communities at LBL and BK sites were Acidobacteria, Proteobacteria, Actinobacteria, and Basidiomycota, and their differences were driven by Gemmatimonadetes and Verrucomicrobia. The dominant fungal phyla of LBL and BK sites were Ascomycota, Zygomycota, and Rozellomcota, which differed significantly between the two sites. The microbial communities showed extremely significant differences (p < 0.05), with MC, pH, and nitrogen being the main influencing factors according to RDA/CCA and correlation analysis. Microbial functional prediction analysis across the two sites showed that the relative abundance of advantageous functional groups was significantly different (p < 0.05). The combined results drive us to conclude that the volcanic soil differences in the deposits appear to be the main factor shaping the microbial communities in Wudalianchi (WDLC) volcanic ecosystems.

Forest management changes the physical environments and nutrient dynamics and then regulates the forest productivity. Soil phosphorus (P) availability is critical for productivity in tropical and subtropical forests. However, it was still poorly understood how soil P content and fraction respond to various forest management practices in these regions. Here, we measured the soil total P, available P, and Hedley’s P fractions, including inorganic and organic P (Pi and Po), in subtropical pine plantations treated with understory removal (UR), non-dominant species thinning (NDST) and dominant species thinning (DST) after nine years. Compared to plantations without management (CK), treatments such as UR, NDST, and DST decreased soil total P at 0–10 cm and soil available P at 0–10 cm and 10–20 cm. Increases in resin-Pi, NaOH-Pi, and C.HCl-Pi resulted in a higher total Pi in 0–10 cm (p < 0.05) in treated plots (UR, NDST, and DST) than in CK plots. UR, NDST, and DST treatments increased NaHCO₃-Po and NaOH-Po (p < 0.05) but decreased C.HCl-Po at a depth of 0–10 cm. Regardless of management treatments, soil total P, available P, and P fractions in 0–10 cm showed higher contents than those in 10–20 cm. There were positive relationships between total P and total Po (p < 0.01) and between available P and total Pi. There were also positive relationships between total P, available P, NaHCO₃-Pi, and NaOH-Pi (p < 0.05). In conclusion, forest management such as UR, NDST, and DST decreased soil total P and available P, and transforming soil P fractions to available P will meet the P demand following management in the pine plantations of subtropical China.

Increased soil nutrient availability can promote tree growth while drought impairs metabolic functioning and induces tree mortality. However, limited information is available about the role of nutrients for drought responses of trees. A greenhouse experiment was conducted with sessile oak (Quercus petraea) and Scots pine (Pinus sylvestris) seedlings, which were subjected to three fertilization treatments in the first year and two water regimes in the second year. Old and newly fixed carbon and nitrogen allocation were traced by dual labeling with ¹³C and ¹⁵N tracers, respectively, at two time points. Leaf gas exchange, biomass, as well as nitrogen and nonstructural carbohydrate (NSC) concentrations of all organs were measured. Fertilization predisposed sessile oak to drought-induced mortality, mainly by prioritizing aboveground growth, C and N allocation, reducing root NSC concentrations and decreasing old C contribution to new growth of leaves. In contrast, fertilization did not additionally predispose Scots pine to drought, with minor effects of fertilization and drought on newly fixed and old C allocation, tissues N and NSC concentrations. The role of nutrients for drought responses of trees seems to be species-specific. Therefore, we suggest nutrient availability and species identity to be considered in the framework of physiological mechanisms affecting drought-induced mortality.

The effects of rising atmospheric CO₂ concentrations (C_a) with climate warming on intrinsic water-use efficiency and radial growth in boreal forests are still poorly understood. We measured tree-ring cellulose δ¹³C, δ¹⁸O, and tree-ring width in Larix dahurica (larch) and Betula platyphylla (white birch), and analyzed their relationships with climate variables in a boreal permafrost region of northeast China over past 68 years covering a pre-warming period (1951–1984; base period) and a warm period (1985–2018; warm period). We found that white birch but not larch significantly increased their radial growth over the warm period. The increased intrinsic water-use efficiency in both species was mainly driven by elevated C_a but not climate warming. White birch but not larch showed significantly positive correlations between tree-ring δ¹³C, δ¹⁸O and summer maximum temperature as well as vapor pressure deficit in the warm period, suggesting a strong stomatal response in the broad-leaved birch to temperature changes. The climate warming-induced radial growth enhancement in white birch is primarily associated with a conservative water-use strategy. In contrast, larch exhibits a profligate water-use strategy. It implies an advantage for white birch over larch in the warming permafrost regions.