This research examined the different response of tree growth to climate change at the early, middle, late and matured successional stages of Korean pine (Pinus koraiensis) and broadleaf mixed forest.

This research used dendroecological methods to analyze radial growth at different successional stages of Korean pine forests in response to climatic change in the Shengshan Nature Reserve of Heilongjiang.

Chronology statistics indicated that the sensitivity of radial growth to inter-annual climate variability decreased from early to later successional stage. Meanwhile, the influence of some climate indices to radial growth also changed during the successional process. Radial growth of matured forest was positively related to mean monthly temperature in June and December of previous year, revealing an obvious “lag effect” of temperature. The ring-width of matured forest had a negative correlation with mean monthly temperature but a positive correlation with monthly precipitation in June of current year, reflecting the limiting role of growing season water availability. However, these limiting effects gradually disappeared towards the earlier stages of forest succession. On the contrary, the growth of early successional forest was negatively correlated to precipitation in June of previous year, and this effect disappeared towards the later successional stages. These differences revealed increased demand of water by dominant species from early to later successional stages. A moving correlation analysis showed that the increased warming and drying climate in the research area had both positive and negative influences on radial growth of each forest type. Earlier successional forests did not show clear long-term growth responses, but Korean pine forests had decreased radial growth in the past decades due to reduced water availability. Climate warming and drying in the future may impose negative impact on the growth, succession and distribution of Korean pine forests.

Forest fire plays a complex and important role in affecting forest regeneration, tree growth, and stand development. Despite the importance of forest fire in modulating forest dynamics, researches on the response patterns of trees of different age-classes to fire disturbances are scarce. This study was conducted to determine the growth patterns of surviving trees of different age-classes in an alpine pine (Pinus densata) forest in the southeastern Xizang Plateau, where a moderate surface fire occurred in 2005.

We collected tree-ring samples of P. densata in the Gong-Zi-Nong valley in Nang County, Xizang Autonomous Region, in western China. Based on the diameter at breast height (DBH), the sampling trees were divided into saplings (DBH < 10 cm) and mature trees (DBH ≥10 cm). The tree-ring samples were subsequently polished, measured, cross-dated, and detrended to produce sequences of tree-ring width indices. The detrended tree-ring sequences were averaged using bi-weight robust method to develop chronologies for saplings and mature trees separately. Pearson correlation coefficients and response coefficients between the sequences of tree-ring width indices and climate factors (air temperature and precipitation) were calculated for examination of the responses of tree-ring sequences to monthly mean air temperature and monthly total precipitation both before and after the fire event. Indices of growth resistance and growth recovery were calculated based on the relative changes of trees’ raw ring width before and after the fire event, for trees in different age-classes. These indices were then compared between the trees in different age classes to assess the impacts of fire on trees.

Before the fire event, the radial growth of saplings showed a significantly negative response to the monthly mean minimum temperature of the preceding November, whereas the radial growth of mature trees showed a significantly positive response to monthly mean minimum temperature and monthly mean temperature of current September; following the fire event, radial growth of both the saplings and the mature trees showed a significantly negative response to monthly mean temperature and monthly mean maximum temperature of January of the tree-ring formation year. Based on the ratios of mean tree-ring widths of 5 post-fire years to those of 5 pre-fire years, the mature trees were significantly more fire resistant than the saplings. Moreover, the mature trees also showed greater ability in post-fire recoveries than the burnt saplings. Our results demonstrated that moderate surface fire stimulated the radial growth of both saplings and mature trees, and that the mature trees better recovered from the fire event than the saplings. The changes in growth-climate relationships following the fire event may attribute to changes in understory vegetation and microenvironments.

Under elevated atmospheric CO₂ concentration, an increase in the net primary production is likely to enhance the amount of litter inputs to forest soil. This study aims to determine the dynamics of soil respiration and soil carbon pool as affected by increased litterfall production.

A litterfall manipulation experiment was conducted in Cunninghamia lanceolata plantations and secondary Castanopsis carlesii forest stands in Chenda township of Sanming in Fujian Province, China, from January 2013 to December 2014, with treatments of litterfall exclusion, litter addition, and control (normal litterfall condition).

(1) The value of temperature sensitivity index (Q₁₀) shows a positive relationship with soil water content in the range 10%-25%, and drops below 1 at water content < 10%. Drought stress altered Q₁₀ value and interrupted the coupling between temperature and soil respiration, as it reduced the diffusion of soluble carbon substrate and the extracellular enzymes, consequently, limited the microbial activity. (2) Linear regression analysis shows that soil respiration is significantly correlated with monthly litter mass (p < 0.05). In the treatments of the control and litter addition in the Cunninghamia lanceolata stands and that of the control in the Castanopsis carlesii stands, soil respiration was best correlated with litter mass two months ago; in the treatment of the litter addition in the Castanopsis carlesii stands, soil respiration was best correlated with litter mass of the current month. (3) On average, the annual CO₂ efflux was significantly reduced by litterfall exclusion, by about (362.0 ± 64.9) g C·m^-2·a^-1 in the Castanopsis carlesii stands and (96.2 ± 37.3) g C·m^-2·a^-1 in the Cunninghamia lanceolata stands compared with the control. Litter respiration contributed to 34.4% of soil respiration in the Castanopsis carlesii stands and 15.1% in the Cunninghamia lanceolata stands. Litter addition increased the soil respiration rate in both Castanopsis carlesii and Cunninghamia lanceolata stands, but the magnitude of the increase did not match up with the doubling of litter inputs, implying that under elevated atmospheric CO₂ concentration, an increased litterfall inputs due to increases in the net primary production would be advantageous to the forest soil carbon sequestration.

Stump plays crucial roles in maintaining soil fertility, sequestering carbon, nursing biodiversity, and conserving soil and water in plantation ecosystems. However, little is known about the decay of stump and the related roots in Pinus massoniana plantations. This study aims to explore the characteristics of stump stock and decomposition in the P. massoniana plantation.

Based on log file records of P. massoniana plantation from Laifu Forestry Management Institute in Yibin City of Sichuan Province, we established a chronosequence of decaying P. massoniana stumps from 1999 to 2013. We then investigated the stock and density of stump wood (SW), bark (B), stomp root (SR), and linked roots with different diameters (R1: 0 mm < diameter ≤10 mm; R2: 10 mm < diameter ≤25 mm; R3: 25 mm < diameter ≤100 mm; R4: diameter > 100 mm).

In the investigated P. massoniana plantations, the stump stocks ranged from 5 to 58 t·hm^-2, stocks in stump wood was the largest, in stump root as the second, and in bark was the smallest, which decreased with the decomposing time. Correspondingly, stump density decreased with decomposing time, while the changes in density varied with stump wood, stump root and roots with different diameters. The decomposition constants of stump wood, bark and stump root were estimated at 0.061, 0.027 and 0.036, respectively. The decomposition constants of roots were estimated to be 0.079 for R1, 0.042 for R2, 0.047 for R3 and 0.119 for R4, respectively. In conclusion, the P. massoniana plantation has a high stock, but decomposes slowly and the decomposition constant varies greatly with stump components in the P. massoniana plantation, which provides certain theoretical basis for the sustainable management of P. massoniana plantation in the region.

We explored α and β species diversity, functional diversity and phylogenetic diversity distribution patterns in three tropical cloud forests along environmental gradients in air temperature and precipitation.

We sampled plots in three tropical cloud forests which are located in the west (Bawangling, 21 plots, BWL), the southwest (Jianfengling, 12 plots, JFL), and the central of Hainan Island (Limushan, 15 plots, LMS). We collected species data and functional trait data including plant height, specific leaf area, chlorophyll content, leaf thickness and wood density. We assessed the differences within- and among-community species diversity, functional diversity and phylogenetic diversity in these three tropical cloud forests using the Kruskal-Wallis test.

The tropical cloud forests in JFL had the highest species abundance and richness whereas the lowest in LMS. However, the Bray-Curtis and Jaccard dissimilarity coefficients showed the opposite distribution patterns (i.e. the highest in LMS whereas the lowest in BWL). Distinct distribution patterns in species diversity across the three tropical cloud forests may be explained by the air temperature and relative humidity. The functional evenness (FEve) within communities was the highest while functional richness (FRic), Rao’s quadratic entropy (RaoQ) and the mean pairwise trait distance among communities were the lowest in JFL, indicating that habitat filtering plays an important role in community assembly. BWL had the highest RaoQ and mean pairwise trait distance among communities, and the lowest FEve, which demonstrated that limiting similarity would be prevalent in forest communities assembled. LMS had the highest FRic within communities and mean nearest trait distance among communities, leading to a limiting similarity influencing forest communities. BWL had the highest Faith phylogenetic diversity (PD) within communities and mean nearest phylogenetic distance among communities, reflecting an overdispersed pattern in phylogenetic structures. LMS had the lowest PD and mean pairwise phylogenetic distance within and among communities, suggesting that a clustered pattern in phylogenetic structures. The mean pairwise phylogenetic distance within and across communities were the highest in JFL while the mean nearest phylogenetic distance within communities was the lowest, indicating that phylogenetic clustering and overdispersion patterns co-occur in this forest. We conclude that both plant species interactions and environmental filtering determine the distribution patterns of plant species diversity, functional diversity and phylogenetic diversity both within and among three tropical cloud forests in Hainan Island.

Nitrogen (N) mineralization is an important ecological process which determines soil N supplying ability, and it is a key research domain of soil N cycling worldwide at present. Nutrient addition can play a key role in regulating soil N transformations. The objective of the study was to evaluate the effects of different levels of N and P additions on in situ N mineralization during growing seasons in the temperate grasslands.

We conducted an field N and P fertilization addition experiment in the temperate grassland in Nei Mongol in June 2014. Five levels of N (0-25 g N·m^?2·a^?1), five levels of P (0-12.5 g P₂O₅·m^-2·a^-1) addition treatments, and a control were set up. We measured the in situ net mineralization rate, ammonification rate, and nitrification rate using the resin core incubation technique once a month from July to October 2014. Aboveground biomass and some selected soil chemical and microbial properties were also measured in the study.

High nitrogen addition did significantly affect the contents of inorganic N. High N addition levels (25 g N·m^?2·a^?1 + 1 g P₂O₅·m^-2·a^-1 and 10 g N·m^?2·a^?1 + 1 g P₂O₅·m^-2·a^-1) significantly increased soil inorganic N content, and the 25 g N·m^?2·a^?1 + 1 g P₂O₅·m^-2·a^-1 treatment markedly increased soil nitrate- (NO₃^- -N) and ammonium-N (NH₄⁺ -N). Compared to N addition, P addition had limited effects on soil inorganic N, NO₃^- -N and NH₄⁺ -N. Only the 12.5 g P₂O₅·m^-2·a^-1 + 2 g N·m^?2·a^?1 treatment significantly increased soil ammonium-N and inorganic N. N addition did significantly affect microbial N transformation rates. The 25 g N·m^?2·a^?1 + 1 g P₂O₅·m^-2·a^-1 treatment significantly stimulated soil net N nitrification rate, mineralization rate and ammonification rate, suggesting that high N addition can effectively improve soil available N supply. N was a limiting factor to soil organic N mineralization in the study area. P addition had negligible effects on soil net N mineralization and nitrification rates, and only the 12.5 g P₂O₅·m^-2·a^-1 + 2 g N·m^?2·a^?1 treatment significantly enhanced ammonification rate in the middle of growing season. The results also indicated that impacts of P addition on soil N mineralization were weaker than impacts of N. Moreover, N and P addition significantly increased aboveground biomass. Under the N and P addition, soil moisture was significantly correlated with net mineralization and nitrification rate, which suggested that it was one of the dominant factors affecting N. Net N mineralization and nitrification rate under N fertilization was significantly correlated with environmental factors (soil organic C, soil C/N and soil total N). Soil N mineralization was not positively correlated with the soil microbial biomass N or C.

In wetlands, water levels can fluctuate, which often disturbs local organisms, such as aquatic plants. The responses of Alternanthera philoxeroides, Myriophyllum aquaticum, and Ludwigia adscendens to water level fluctuations of different frequencies were examined here.

Water level fluctuations were simulated at four frequencies: static (0 frequency), one cycle (1 frequency), two cycles (2 frequency), and four cycles (4 frequency), and with fluctuation amplitudes (± 25 cm) during a 60 day experiment. Morphological and physiological traits of plants, including branching number, shoot length, total biomass, shoot root ratio, chlorophyll content, and maximum PSII quantum efficiency(F_v/F_m) were assessed.

Water level fluctuation was found to have no significant impact on branching number, root shoot ratio, or F_v/F_m of A. philoxeroides,but all scenarios except 1 frequency were significantly associated with longer shoots and lower total biomass and chlorophyll content. The traits of M. aquaticumshowed different responses to water level fluctuation: branching number and F_v/F_m showed no changes, but shoot length (2 frequency) and root shoot ratio (1 and 4 frequency) increased significantly, and total biomass and chlorophyll content (expect 4 frequency) decreased. In L. adscendens, water level fluctuation was associated with lower branching number in all scenarios except 2 frequency, shoot length in all scenarios except 1 and 2 frequency, total biomass in all scenarios except 2 frequency, and chlorophyll content but had no significant effects on root shoot ratio or F_v/F_m. Under most water level fluctuation conditions, the branching number, shoot length, total biomass, chlorophyll content, and F_v/F_m of L. adscendens were significant higher than those of A. philoxeroides and M. aquaticum, and the latter two had no significant differences.

suggested that water level fluctuations were the limiting factor for the growth of three species in autumn. Alternanthera philoxeroides and M. aquaticumdid not show higher invasiveness in environments in which the water level fluctuated in autumn but did show higher tolerance and plasticity in response to water level fluctuations in general. This was related to the invasiveness of introduced species.

also indicated that preventive efforts focusing on potential invasion by M. aquaticum should be strengthened.