Warming may have profound effects on nitrogen (N) cycling by changing plant N demand and underground N supply. However, large uncertainty exists regarding how warming affects the integrated N dynamic in tropical forests. We translocated model plant‐soil ecosystems from a high‐altitude site (600 m) to low‐altitude sites at 300 and 30 m to simulate warming by 1.0°C and 2.1°C, respectively, in tropical China. The effects of experimental warming on N components in plant, soil, leaching, and gas were studied over 6 years. Our results showed that foliar δ15N values and inorganic N (NH4‐N and NO3‐N) leaching were decreased under warming, with greater decreases under 2.1°C of warming than under 1.0°C of warming. The 2.1°C of warming enhanced plant growth, plant N uptake, N resorption, and fine root biomass, suggesting higher plant N demand. Soil total N concentrations, NO3‐N concentrations, microbial biomass N and arbuscular mycorrhizal fungal abundance were decreased under 2.1°C of warming, which probably restricted bioavailable N supply and arbuscular mycorrhizal contribution of N supply to plants. These changes in plants, soils and leaching indicated more closed N cycling under warming, the magnitude of which varied over time. The closed N cycling became pronounced during the first 3 years of warming where the sustained reductions in soil inorganic N could not meet plant N demand. Subsequently, the closed N cycling gradually mitigated, as observed by attenuated positive responses of plant growth and less negative responses of microbial biomass N to warming during the last 3 years. Overall, the more closed N cycling under warming could facilitate ecosystem N retention and affect production in these tropical forests, but these effects would be eventually mitigated with long‐term warming probably due to the restricted plant growth and microbial acclimation.

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Over the past 30 years, global surface temperature has increased by approximately 0.2°C per decade (IPCC, 2018). Clearly, the increase in temperature can affect tree growth and mortality (Bowman et al., 2014; Liu et al., 2016), influencing forest structure and composition in tropical forests (Zhou et al., 2013, 2014). The response of trees to warming depends on whether they can adjust their phenotypic traits; for example, many tree species maintain enhanced growth by increasing photosynthetic capacity (Drake et al., 2015). However, few studies address leaf hydraulic and economic traits, combined with related phenotypic plasticity, in long-term field warming experiments (Grady et al., 2013). Leaf hydraulic traits, such as leaf hydraulic conductance (K leaf), stomatal conductance (g s) and stomatal anatomical traits, play a vital role in regulating leaf gas exchange. K leaf measures water flow efficiency through the leaf, defining leaf water transport capacity (Locke et al., 2013). Under warmer conditions, higher K leaf may increase

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& Key message In a downward transplantation experiment, warming stimulated growth and photosynthesis of Schima superba Gardn. et Champ., Syzygium rehderianum Merr. et Perry and Itea chinensis Hook. et Arn. via increased stomatal conductance. Warming had no effect on growth of Machilus breviflora (Benth.) Hemsl., indicating species-specific differences in response to warming. & Context Climate change has been shown to shift species composition and community structure in subtropical forests. Thus, understanding the species-specific responses of growth and physiological processes to warming is essential. & Aims To investigate how climate warming affects growth, morphological and physiological performance of co-occurring tree species when they are growing at different altitudes. & Methods Soils and 1-year-old seedlings of four subtropical co-occurring tree species (Schima superba Gardn. et Champ., Syzygium rehderianum Merr. et Perry, Itea chinensis Hook. et Arn. and Machilus breviflora (Benth.) Hemsl.) were transplanted to three altitudes (600 m, 300 m and 30 m a.s.l.), inducing an effective warming of 1.0°C and 1.5°C. Growth, morphological, and physiological performances of these seedlings were monitored. & Results When exposed to warmer conditions, aboveground growth of the four species except M. breviflora was strongly promoted, accompanied by increased light-saturated photosynthetic rate and stomatal conductance. Warming also significantly increased concentrations of non-structural carbohydrates in leaves of S. rehderianum and M. breviflora, stems of S. superba and S. rehderianum, and roots of I. chinensis. However, we did not detect any effect of warming on stomatal length and stomatal density. & Conclusion Our results provide evidence that climate warming could have species-specific impacts on co-occurring tree species, which might subsequently shift species composition and forest structure.

Sensitivity to climate change is one of the key features of the Dinghushan National Nature Reserve that is located in the lower subtropical China. Having faced typhoon Mangkhut in 2018, there emerged a need to study the effects that the typhoon had on the evergreen broad-leaved forest community in Dinghushan. The forest composition data for 2015, 2018, and 2020 was used in this study. The aim was to establish a scientific basis for the restoration of natural forests that have the ability to withstand strong weather phenomena such as typhoons and the hypothesis stated that typhoon Mangkhut had a long-term detrimental effect on the forest community in Dinghushan forest. The results showed that trees that have a DBH of less than 5 cm and a height of less than 2 m were more prone to damage during a severe weather events. In 2015, there was a total of 5,682 trees per hectare while in 2018 there was a total of 5,022 trees per hectare showing a decline in the number of trees per hectare of 660 due to the typhoon. Number of trees in each DBH class, height class, total above ground dry weight and average tree height was also lower in 2018 as compared to 2015 and 2020. The species abundance was also adversely affected with a loss of 672 species per hectare in 2018 compared to 2015. In 2020, about 83% of all trees had a DBH of less than 5 cm and an average height of 3.8 m making up a large proportion of trees that could be damaged if another storm occurred of similar or greater magnitude as the one that hit the region in 2018. Of interest was the forests remarkable ability to bounce back as there is an increase in biomass when 2018 is compared to 2020. The results support the hypothesis of the study. It is therefore of utmost importance that strategies be put in place to protect this ecosystem and others of a similar nature, by employing the use of natural forests that have great resilience against typhoons.

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& Key message N addition (56, 156, and 206 kg N ha −1 yr −1 as dissolved NH 4 NO 3) method (canopy vs soil) did not affect the biomass of N 2-fixers (Acacia mangium Willd. and Ormosia pinnata Lour.), but significantly affected the biomass of non-N 2-fixers (Schima superba Gardner & Champ., Pinus massoniana Lamb.). Coniferous species exposed to N addition on the canopy rather than the soil had higher N accumulation. & Context Previous experiments simulating nitrogen (N) addition in forests were conducted by adding N fertilizer directly to soils, which neglects the fact that N uptake can be done by canopy leaves. & Aims The objective of this study is to examine how different N addition methods (canopy vs soil) affect growth and N accumulation of four subtropical tree seedlings. & Methods An open-air greenhouse experiment was conducted to expose four tree species (Schima superba Gardner & Champ., Pinus massoniana Lamb., Acacia mangium Willd. and Ormosia pinnata Lour.) to different N addition methods (canopy or soil) and N levels (ambient, medium, or high). & Results N addition method affected the biomass of non-N 2-fixers (Schima superba Gardner & Champ. and Pinus massoniana Lamb.), while N 2-fixers (Acacia mangium Willd. and Ormosia pinnata Lour.) were unaffected. N concentrations in the soils and leaves of all trees were significantly increased by the medium and high N additions, and soil N concentrations resulted from N addition via soil rather than the canopy. Although leaf N concentration was significantly affected by N addition method in all trees except for Ormosia pinnata, only N accumulation in Pinus massoniana was significantly affected by N addition method. & Conclusion N addition method affected the biomass of non-N 2-fixers and N accumulation in coniferous species, while it did not affect the biomass of N 2-fixers and N accumulation in broadleaf species.