Aims Rain-use efficiency (RUE), the ratio of vegetation productivity to annual precipitation, is an important measure of water use and a key determinant of the net primary production (NPP) of forest ecosystems. Our objective is to investigate the interannual variation of RUE of three conifer forests and their response to the variation of meteorological factors.
Methods We calculated the biomass and NPP of three coniferous forests (Pinus armandii natural forest, Larix principis-rupprechtii plantation and Pinus tablaeformis plantation) in Liupan Mountains of Ningxia, China by dendroecological methods, empirical biomass equations and collected meteorological data including monthly air temperature, humidity and precipitation. Then we calculated the RUE of these forests and analyzed their correlation with meteorological factors.
Important finding The NPP and RUE of L. principis-rupprechtii plantation, having the values of 6.72 t·hm ^-2·a ^-1and 1.12 g·m ^-2·mm ^-1, respectively, were 1.53 and 1.49 times higher than the Pinus armandii natural forest and 0.17 and 0.15 times higher than the P. tablaeformis plantation, respectively. The RUE increased with forest age when it was younger than 32 years, but RUE varied among species. The interannual variation of RUE of P. armandii natural forest was relatively stable when aged 32-45 years and then decreased with age. With increasing annual precipitation, the RUE of P. armandii natural forest decreased, but the RUE of the two plantations increased at first and then decreased. The RUE of all three forests tended to be similar in the driest years and tended to have the same minimum value in the wettest years. RUE, which was affected by meteorological factors of the previous year, responded to meteorological factors differently among tree species, but it was mainly influenced by meteorological factors of the current year and its annual variation pattern. The RUE of P. armandii natural forest was significantly negatively correlated with precipitation in August of the previous year and that in September, October and November of the current year. The RUE of the two plantations was significantly correlated with precipitation in September of the previous year and that in April of the current year and, in the case of the L. principis-rupprechtii plantation, to precipitation in September of the current year. The RUE of all three tree species was significantly correlated with the mean air temperature in June and March of the current year and that in June of the previous year. In addition, the RUE of P. armandii natural forest was significantly correlated with air temperature in February of the previous year, and the RUE of the two plantations was significantly positively correlated with air temperature in April and May of the current year.

Aims Variation in leaf traits with changing leaf age denotes plant life history strategy and reflects biomass allocation pattern in plant leaves. Our objective was to explore variability and correlation of leaf traits between current-year and former-year leaves for evergreen broad-leaved trees, in order to reveal effects of leaf age on the pattern of construction and cost during development of leaf area.
Methods Our one hectare study site is located in Tiantong National Forest Park (29°52′ N, 121°39′ E), Zhejiang Province. Three key functional traits (mean leaf area (MLA), specific leaf area (SLA) and leaf dry matter content (LDMC)) in each of current-year leaves and former-year leaves were measured for 2277 evergreen trees belonging to 41 species. Variability and correlations for each of three leaf traits were compared between current-year and former-year leaves at both individual and species levels.
Important findings At both individual and species levels, variability coefficients (i.e., CV) were highest in MLA (individual: 79.5%; species: 66.5%), intermediate in SLA (individual: 28.1%; species: 24.7%) and lowest in LDMC (individual: 17.0%; species: 14.1%). Variability coefficients among the three leaf traits were greater in current-year leaves than in former-year leaves. Former-year leaves had significantly greater MLA (t = -38.53, p < 0.001) and LDMC (t = -9.71, p < 0.001), but lower SLA (t = 45.30, p < 0.001) than current-year leaves. At the individual level, the values for MLA, SLA and LDMC in current-year leaves explained 86%, 48% and 41% of the total variation for MLA, SLA and LDMC in former-year leaves. More significantly, at the species level 97%, 83% and 85% of the total variation in each of MLA, SLA and LDMC for former-year leaves resulted from variability of MLA, SLA and LDMC from current-year leaves. Variation in SLA between differently aged leaves demonstrated that, at a given unit investment of biomass, a relatively larger leaf area can be structured by current-year leaves than by former-year leaves, thus having a low cost in constructing leaf area for current-year leaves. In conclusion, plant leaf traits vary and connect significantly with change of leaf age. Trade-offs between biomass construction and cost in leaf area production might affect plant leaf development.

Aims Wildfire had been one of the major forces that shaped the earth’s vegetation. However, few studies had documented how winter wildfire affected plant community structure. This study explores the response mechanism of subalpine grassland vegetation to winter wildfire.
Methods We chose subalpine areas of western Sichuan as a research site and selected 18 plots in subalpine grassland with and without winter wildfire. We analyzed community structure with species diversity analysis, TWINSPAN analysis and dry-weight-rank analysis.
Important findings Our study found that winter wildfire did not alter vegetation diversity, evenness, and species richness, but changed species composition. The quantity and biomass of annual grasses, perennial forbs and shrubs increased after winter wildfire. In addition, although the number of perennial forbs decreased, the biomass increased after winter wildfire. Moreover, the number and biomass of perennial grasses decreased, the biomass of graminoid species decreased and the biomass of forbs increased. Overall, winter wildfire decreased the competitive abilities of graminoid, such as Capillipedium parviflorum and Poa sp. Forbs, such as Leontopodium leontopodioides, Artemisia sacrorum and Anemone rivularis, had the advantage of competition for resources. Moreover, the edibility of grass was degraded following fire.

Aims Eucalyptus grandis is an excellent, fast-growing timber species. It is important to understand the effect of nitrogen and phosphorus addition on E. grandis growth, nutrient limitation and stoichiometric characteristics. Our objectives are to test 1) biomass of organs (roots, stems and leaves) and allocation proportion, 2) C, N and P content and allocation in different organs and 3) elements that restrict the growth of E. grandis as well as N and P use efficiency and C:N:P stoichiometry.
Methods We grew E. grandis clone tissue culture seedlings using a pot experiment with acidic purple soil and N and P fertilizer additions. We measured the biomass and C, N and P content of roots, stems, leaves and soils.
Important findings Roots, stems, leaves and total biomass of E. grandis seedlings were significantly affected by application of N, which increased the aboveground biomass ratio and significantly reduced the root biomass ratio. Total biomass was not significantly affected by application of P, root biomass allocation ratio increased significantly and stem and leaf biomass allocation were not significant affected. N or P fertilization significantly changed N and P content and the stoichiometric ratio, as well as significantly affected the soil and plant N:P relationship. N fertilization can promote N uptake and inhibit the absorption of P in acid purple soil, and then P fertilization can promote P uptake of E. grandis seedlings. C, N and P distribution in roots, stems and leaves were significantly affected by N fertilization while not significantly affected by P fertilization. N-use efficiency was reduced and P-use efficiency improved significantly by N addition; however, P-use efficiency was reduced significantly by P addition. N:P of roots, stems and leaves can be significantly improved by N fertilization to alleviate the phenomenon of lack of N, but it is further exacerbated by the lack of N element by P fertilization.

Aims Soil C:N is a sensitive indicator of soil quality and an indicator for assessing carbon and nitrogen nutrition balance of soils. Our objective was to explore the effects of soil C:N on growth and distribution of nitrogen and carbon of Malus hupehensis seedlings.
Methods Using the track technology of C and N double mark, we investigated growth parameters (height, stem diameter and dry matter of different organs), ¹⁵N parameters (absorption, N derived from fertilizer, distribution and utilization) and ¹³C parameters (distribution in different organs) of two-year old M. hupehensis seedlings under six different soil C:N treatments (T1-T6 were 4.70, 9.78, 14.70, 19.96, 25.60 and 28.83, respectively).
Important findings With increase of soil C:N, dry matter of roots increased significantly, while the height, stem diameter and dry matter of above ground parts and total plant increased at first and then decreased. The highest value appeared in the T4 treatment. There were significant differences in ¹⁵N utilization efficiency among the six different treatments. ¹⁵N utilization efficiency increased from T1 to T4, and the rate of T4 (18.46%) was 1.73 times than that of T1. But, the ¹⁵N utilization efficiency decreased with a further increase of soil C:N, as the rate of T5 and T6 reduced that of T4 by 1.59% and 2.58%, respectively. In the two lower soil C:N treatments (T1 and T2), the order of Ndff value ( ¹⁵N derived from fertilizer) in the organs was roots > leaves > stems. With increase of soil C:N, Ndff value in leaves was the highest, followed by roots and stems. ¹⁵N distribution ratio in leaves increased, while ¹³C distribution decreased with increase of soil C:N, but the changes were the opposite in roots. Considering plant growth and utilization of nitrogen, the suitable soil C:N was 21-23 under these experimental conditions.

Aims The objective was to investigate exogenous glutathione (GSH) mitigation effects of Cadmium (Cd) toxicity on ground cover plants.
Methods A greenhouse pot experiment was conducted to explore the effects of spraying different concentrations (0, 20, 40, 60, 80 and 100 mg·L ^-1) exogenous GSH on Dianthus chinensis seedlings exposed to 50 mg·kg ^-1 Cd in the soil.
Important findings 50 mg·kg ^-1 Cd significantly inhibited the growth of D. chinensis seedlings; however, a range of concentrations of sprayed exogenous GSH significantly relieved Cd stress on D. chinensis seedlings. Sprayed D. chinensis seedlings had increased activities of the catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), as well as increased ascorbic acid (AsA) and GSH contents, biomass, plant height and number of tillers. There were decreases in malondialdehyde (MDA), cell membrane permeability, Cd contents, O₂· ^- production rates and accumulated amount of H₂O₂. However, with increased exogenous GSH concentration, there was a downward trend in mitigation effects. Considering all factors, the mitigation effects were maximized by spraying 55-65 mg·L ^-1 exogenous GSH.

Aims Triploid Populus tomentosa, a main clone for pulpwood forestry in the North China Plain, is usually planted using a wide- and narrow-row spacing planting schemes (WNRPS). Our objectives were to make water and fertilizer management recommendations for P. tomentosa under a WNRPS based on root form characteristics, and determine the relationship between the vertical distribution of P. tomentosa fine roots (FR) and soil nutrient factors.
Methods We obtained 2106 soil samples by soil coring down to 150 cm depth around eight sample trees in a five-year-old P. tomentosa plantation located in Gaotang County, Shandong Province, China. The samples were used to measure root distribution, organic matter (OM), available P and alkaline N content.
Important findings FR biomass density (FRBD) in the wide row zone (WRZ) decreased with increasing depth in the 0-30 cm soil, but was distributed evenly below 30 cm depth (p = 0.079). The vertical FRBD profile in the narrow row zone (NRZ) showed a bimodal pattern. In different layers at 10-150 cm depth, FRBD in the NRZ was 17%-148% higher than in the WRZ. With increasing depth in both WRZ and NRZ, coarse root biomass density (CRBD) increased and then decreased. However, the FRBD to CRBD ratio (F/C) varied slightly with depth (p > 0.05), and the mean F/C in the NRZ was 60% higher than that in the WRZ. Horizontally, in both WRZ and NRZ, the FRBD distribution was almost even, while the CRBD and F/C decreased and increased, respectively, with increasing distance from the trunk. On a two dimensional scale, the FRBD distribution within the NRZ was relatively even, but FR were mainly concentrated in surface soil within the WRZ. CRBD was distributed asymmetrically around the trunk. The ranges of 0-20 cm depth and 160-300 cm distance from the tree were the areas with high mean FRBD and F/C in the WRZ, which were 1.8 and 0.1 times larger than the mean values of corresponding variables in the WRZ, respectively. FRBD scaled positively with OM, available P and alkaline N content at 0-30 cm depth, but showed no obvious trend with respect to soil characteristics below 30 cm depth. In conclusion, the differences in P. tomentosa root distribution between WRZ and NRZ were reflected in the one-dimensional vertical FR distribution and two-dimensional FR and coarse roots distribution. OM, available P and alkaline N were key controls on the vertical FR distribution at 0-30 cm depth, but had no effects on FR distribution below 30 cm depth. For P. tomentosa plantations under WNRPS, water should be provided mainly to the NRZ, and slow- and fast-release fertilizer should be supplied to the shallow soil in the area near the wide row center and in the NRZ, respectively.

Aims Despite numerous dendroclimatological and dendroecological studies conducted over many regions around the world, associated research on the mechanism of how tree species respond to climate change rarely have been reported. In order to explore the climate-growth patterns in detail, observations of cambial activities have been widely used for physiological and ecological insights.
Methods By investigating seasonal dynamics of cambial activities of five different tree species like Sabina przewalskii, Betula albo-sinensis, Pinus tabuliformis, Picea crassifolia, and Picea wilsonii, we improved the pre-existing technique using plant paraffin sections.
Important findings We considered the process of softening and the timing control of dehydration, cleaning, wax-dipping and staining to improve cambial slices and thereby a provide reliable foundation of paraffin sections of lignified samples useful to the domains of dendroclimatology, dendroecology and wood anatomy.