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There are significant differences in the morphological and physiological responses of larch species with contrasting growth rates under fertilization. However, little is known about species-specific differences in responses to nutrient imbalance caused by fertilization. Therefore, in this study, the effects of nitrogen (N) and phosphorus (P) fertilization on the morphological, physiological and chloroplast ultrastructural traits of two contrasting larch species, fast-growing Larix kaempferi and slowly-growing L. olgensis , grown in larch plantation soil, were investigated during two growth seasons. It was shown that N and combined N and P (NP) fertilization increased plant photosynthesis, foliar N contents, chlorophyll contents, and dry mass accumulation and partitioning in aboveground organs in both larch species. Although P fertilization enhanced P accumulation, its presence reduced the N content in soluble proteins in the foliage of both larch species. Yet, P fertilization exhibited some differences in the two species: P fertilization increased photosynthesis, chlorophyll content and biomass accumulation of L. olgensis , while it decreased these parameters dramatically in L. kaempferi. P fertilization increased foliar N content in L. olgensis , while it reduced it in L. kaempferi . P fertilized L. kaempferi had more damaged chloroplast ultrastructure than L. olgensis . In addition, L. kaempferi exhibited lower acid phosphatase activities, and higher photosynthesis and biomass accumulation than L. olgensis , except under P fertilization. L. kaempferi allocated more biomass into needles, except under P fertilization, while L. olgensis allocated more into stems under fertilization. In conclusion, it was shown that nutrient imbalance caused by P fertilization has greater negative effects on a fast-growing species than on a slowly-growing one, and the negative effects are related to differences in acclimation strategies, N partitioning to photosynthetic components, and P transportation and metabolism in the foliage. [ABSTRACT FROM AUTHOR]

Non-structural carbohydrates (NSC) are critical to plant signaling, gene transcription, physiological processes, survival and growth. Previous studies have demonstrated that species differing in NSC contents have various responses to stressful environments. However, effects of intra- and interspecific competition or N fertilization on NSC have not been previously studied. We employed two coniferous tree species, Larix kaempferi and Larix olgensis , to investigate the effects of intra- and interspecific competition on NSC under two N supply levels, with and without N fertilization. N fertilization significantly promoted the growth rates, biomass accumulation, carbon isotope composition and N concentration of leaves of the two species. Competition patterns significantly affected the average root diameter. Interspecific competition tended to increase the specific root length and specific root tip density. Also, interspecific competition significantly increased the N concentration of leaves but declined their C:N ratio under no N fertilization (N−) treatments. L. kaempferi greatly benefited from the presence of L. olgensis , particularly under N fertilization (N+) treatments. Competition patterns, N fertilization and their interactions promoted N and carbohydrate storage. Our results demonstrated that N was a crucial factor to drive and regulate carbon balance. Differences between species in carbohydrate metabolism may contribute to their coexistence or niche differentiation. [ABSTRACT FROM AUTHOR]

Highlights: [•] A four-year field experiment was conducted in a fir forest using the OTC method. [•] Soil warming accelerated labile C decay and increased recalcitrant C pools. [•] Soil warming did not influence the respiration quotient at either elevation. [•] Altitude significantly affected soil C fractions. [•] The high altitude was more responsive to soil warming than the low altitude. [Copyright &y& Elsevier]

Abstract: To examine whether deciduous and evergreen tree species differ in their performance and plastic responses to elevated atmospheric CO2 and temperature, we investigated growth, leaf area ratio (LAR), specific root length (SRL), nitrogen uptake efficiency (NUpE) and nitrogen use efficiency (NUE) of Populus yunnanensis and Abies faxoniana grown in environment-controlled chambers. Our results showed that temperature stimulated growth more than did CO2 in both species. The magnitude of temperature and CO2 effects varied between the species, as greater stimulation was detected in A. faxoniana than in P. yunnanensis. Greater responses of A. faxoniana were associated with higher LAR and higher NUE. However, NUpE did not differ between species and could not explain this advantage. On the other hand, the studied species did not differ in their mean overall plasticity (calculated for each species by averaging the indices of plasticity obtained for each of the 17 variables), which, however, was achieved in different ways. Across CO2 and temperature treatments, A. faxoniana exhibited greater plasticity in stomatal conductance, LAR, SRL and NUE, whereas P. yunnanensis exhibited greater plasticity in net photosynthesis rate, leaf respiration and root/shoot ratio. Our results suggested that plasticity of key traits, such as LAR, SRL and NUE, may have important implications for the superiority of A. faxoniana in the response to climate change. Our results highlight the importance of exploring the functional significance of traits rather than the extent of plasticity as potential determinants of interspecific differences in responses to climate change. [Copyright &y& Elsevier]

Abstract: The effects of three watering regimes (100%, 50% and 25% of field capacity, FC) on photosynthetic traits and leaves’ self-protective systems were investigated in Populus cathayana Rehd. males and females. The results showed that drought (25% of FC) caused disorder in photosynthesis, increased the amounts of osmotically active substances (soluble sugars, proteins and proline), accumulation of reactive oxygen species (ROS), changes in antioxidant enzyme activities and damage in the integrity of cellular membranes and chloroplasts in both males and females. However, compared with drought-stressed females, drought-stressed males showed (1) higher values of net photosynthetic rate (P n), maximum rate of electron transport driving RuBP regeneration (J max), maximum rate of RuBP carboxylation (V cmax), carboxylation efficiency (CE) and non-photochemical quenching coefficient (qP); (2) higher contents of soluble proteins and proline; (3) higher activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and polyphenoloxidase (PPO); (4) less negative effects on cellular membranes and chloroplasts. These results indicate that P. cathayana males have a better self-protection of the photosynthetic system, greater accumulation of substances for osmotic adjustment and a more efficient enzymatic detoxification cycle for eliminating the negative effects caused by ROS under drought stress than do females. [Copyright &y& Elsevier]

Abstract: In all, 48 sites of subalpine coniferous forest that had undergone natural regeneration for 5–310 years were selected as study locations in the Southwest China. We compared species richness (S), plant diversity (Shannon–Wiener index, H′; Margalef index, R), and above- and below-ground ecosystem carbon (C) pools of six plant communities along a chronosequence of vegetation restoration, and we also examined evidence for a functional relationship between plant diversity and C storage. Our results showed that above-ground C increased significantly (over 52-fold), mainly due to the increase of C in aboveground living plants and surface litter. Soil organic carbon (SOC) content increased from the herb community type (dominated by Deyeuxia scabrescens, P1) to mixed forest type (dominated by Betula spp. and Abies faxoniana, P4), which constituted the main C pool of the system (63–89%), but decreased thereafter (communities P5–P6). The mean C stock in the whole ecosystem – trees, litter layer and mineral soil – ranged from 105 to 730MgCha−1 and was especially high in the spruce forest community type (dominated by Picea purpurea, P6). On the other hand, the relationships between C stocks (soil, aboveground) and mean annual temperature or altitude were generally weak (P >0.05). Moreover, we did not detect a relationship between S and aboveground C storage, while we found a significant negative relationship between H′, R and aboveground C storage. In addition, our experiment demonstrated that total root biomass and litter C/N ratio were significant functional traits influencing SOC, while S, R, and H′ had little effect. Path analysis also revealed that litter C/N ratio predominantly regulated SOC through changes in the quantity of microorganisms and soil invertase enzyme activity. [Copyright &y& Elsevier]

• Sexual dimorphism was present in phenolic metabolites of roots. • Females showed greater biochemical plasticity in response to different-sex neighbors. • Mixed-sex plantations had more diverse microbial communities in rhizosphere. • Phenolic metabolites may cause selective pressure that shapes microbial communities. We assessed root phenolics and rhizosphere microbiomes of Populus cathayana females and males in the replicated 30-year-old plantations, including pure female plantations (PF), pure male plantations (PM), and mixed female and male plantations (MS) to reveal sex and neighbor effects, and associations between root phenolic metabolites and root-related microbes. The phenolic composition of females varied more between intrasexual and intersexual interactions compared to that of males. Thus, sexual dimorphism was present in the metabolic composition and biochemical plasticity. MS plantations enhanced the bacterial and fungal alpha diversity of both females and males. The composition of fungal communities of females and males in MS plantations was different from that in PF and PM, while such differences were not found in the composition of bacterial communities. Bacterial and fungal diversities were correlated with concentrations of specific phenolic metabolites and were most positively responsive to root benzoic acid and pinoresinol production, respectively. Our findings indicate that sex-specific interactions affect the system of plant sex - root phenolics - rhizosphere microbes, and they may contribute to sex-specific resource utilization patterns. Knowledge of such mechanisms would be helpful when establishing plantations of dioecious plants. [ABSTRACT FROM AUTHOR]

Abstract: Birch (Betula albosinensis Burk.) seedlings were grown under two CO2 concentrations, 350μmolmol−1 (ambient CO2) and 700μmolmol−1 (elevated CO2), and in two planting densities, 32plants/m2 (low density, LD) and 72plants/m2 (high density, HD). The objectives were to characterize the responses of leaf photosynthesis to long-term elevated CO2 in birch seedlings in different planting densities, and to assess whether elevated CO2 regulates the photosynthetic capacity of leaves, in terms of nitrogen concentration (N), the activity of ribulose bisphosphate carboxygenase (Rubisco), the photosynthetic efficiency of Rubisco and the concentration of nonstructural carbohydrates (TNC). In both planting densities, the leaves of birch seedlings grown under elevated CO2 but measured at 350μmolmol−1 CO2 had a lower leaf N concentration, net CO2 assimilation rate (A), transpiration (E) and stomatal conductance (g s), and a higher water use efficiency (WUE) than those of birch seedlings both grown and measured under ambient CO2 concentration. On the other hand, the values of A, E, g s and WUE were significantly affected by planting density under ambient CO2, whereas these parameters were not affected by planting density under elevated CO2. In contrast, the levels of sucrose, soluble sugars, starch and TNC in the leaves were not significantly affected by planting density under ambient CO2, whereas these parameters were significantly affected by planting density under elevated CO2. Our results demonstrated that there are different acclimations of leaf photosynthesis in birch seedlings, as affected by elevated CO2 and planting density, and they highlighted the importance of the CO2 level and planting density for the physiological ecology of woody plants. [Copyright &y& Elsevier]

Abstract: Cuttings of Populus kangdingensis and P. cathayana originating from high and low altitudes in south-west China, respectively, were used to determine the effect of drought and enhanced UV-B radiation and their combination on plant growth and physiological traits in a greenhouse during one growing season. In both species, cuttings grown under drought conditions exhibited reduced growth and more abscisic acid (ABA) accumulation than did plants kept under well-watered conditions. Enhanced UV-B radiation significantly reduced plant growth and influenced ascorbate peroxidase (APX) activity, proline concentration, the amount of UV-B absorbing compounds and carbon isotope composition (δ 13C) in both species, while it hardly affected ABA accumulation. However, partial differences in responses to each stress were observed between the two species. In P. cathayana, the additive effect of both stresses on plant height and leaf area was observed, and drought significantly increased the free proline concentration. In contrast, distinctly higher APX activity, and ABA and δ 13C levels were observed in P. kangdingensis when compared to P. cathayana. Moreover, an increase in the amount of UV-B absorbing compounds was detected in P. kangdingensis both after the treatment with UV-B alone as well as after its application to drought-stressed plants. In P. cathayana, superoxide dismutase (SOD) activity showed a significant increase under enhanced UV-B, while a pronounced increase in the amount of UV-B absorbing compounds was observed only under the combination of the two stresses. Our results suggest that P. kangdingensis, originating from high altitude and being apparently adapted to drought and high levels of UV-B, exhibits greater tolerance to drought and enhanced UV-B radiation than does P. cathayana originating from lower altitude. [Copyright &y& Elsevier]

• Sex significantly affects water content, NO 3 −, total N and total P of rhizosphere. • Bacteria in bulk and rhizosphere are more strongly affected by sex than fungi. • Higher soil moisture in female rhizosphere promotes N-cycling related bacteria. • More Actinobacteria in rhizosphere contribute to higher N use efficiency of male. Plant-soil microbe interactions are determined by plant characters. Sexual dimorphism in root development, nitrogen (N) assimilation and resource allocation have been studied in different environments. However, how dioecious plants affect soil microbial communities in natural forests, particularly in low precipitation regions, is still poorly known. In this study, natural Populus euphratica forests were investigated in three arid regions. We hypothesized that males and females impose sex-specific impacts on physiochemical traits of soil, microbial communities and N-cycling processes. We discovered only little sex effect on most physiochemical traits, and bacterial and fungal communities in top soil (0–20 cm) in the three studied forests. However, the sex effect was greater in deep soil. Compared with fungi, the structure and composition of bacterial communities were affected more by plant sex in the rhizosphere and bulk soil. Sex indirectly affected N-cycling processes through a negative impact on the soil water content. Expressions of AOA, AOB, nifH , nirS and nirK in the rhizosphere soil were significantly affected by sex, forest site and their interactions. Proteobacteri a, Actinobacteria and Firmicutes in the rhizosphere and bulk soils of P. euphratica males showed more significant effects on ammoxidation, N fixation, denitrification and protease activities when compared to females. The results suggest that sexual differences in shaping bacterial communities and affecting N-cycling processes are greater when the soil becomes drier. Thus, low precipitation causes intense sex differences in the nitrogen uptake and use efficiency. Our study highlights the importance of sexual effects on shaping specific microbial communities and N-cycling processes. [ABSTRACT FROM AUTHOR]

• Inter- and intra-sexual competition patterns affected eco-physiological responses of P. cathayana to EC, ET and ETC. • Carbon-related metabolites of females were most strongly affected by ET under inter- and intra-sexual competition. • Males exhibited strongest responses of water and nitrogen use efficiencies to EC and ETC. • Competitive pressure of females on males was intensified by ET but alleviated by ETC. It remains unclear how global climate change affects dioecious plants that may be especially vulnerable to climate drivers, because they often exhibit skewed sex ratios and eco-physiological specialization in certain microhabitats. In this study, female and male saplings of Populus cathayana were employed to explore sex-specific responses and the effects of sexual competition under elevated temperature (ET), elevated CO 2 (EC) and combination of elevated temperature and CO 2 (ETC). The results demonstrated that elevated temperature and CO 2 interactively modulated sexual competition and responses of P. cathayana. Moreover, competition patterns affected the eco-physiological responses of P. cathayana to climate change treatments. Under both intra- and inter-sexual competition, biomass components, photosynthetic parameters and carbon-related metabolites of females were most strongly affected by ET, while males exhibited a higher photosynthesis and resource use efficiency, and a better biomass accumulation and carbon balance mechanism when compared to females when experiencing intra-sexual competition under EC. The competitive pressure of females on males in inter-sexual competition was intensified by ET, while it was alleviated by ETC. We conclude that climate change drivers and competition patterns differently regulate the sex-specific responses and competitive intensity of males and females, which may have a crucial effect on sex ratios, spatial sexual segregation, biomass production and carbon sequestration in dioecious species in the future. [ABSTRACT FROM AUTHOR]

• P application level and pattern affected the performance of P. deltoides clones. • Root traits and rhizosphere processes varied among P. deltoides genotypes. • Tradeoffs occurred between root morphology and root exudation in low-P soils. • High soil acid phosphatase activity alleviated negative effects of P shortage. • Higher SRL was associated with higher biomass under high/heterogeneous P supply. Soil phosphorus (P) availability and its distribution influence plant growth and productivity. To evaluate strategies that allow genotypes to be efficient under variable P environments, we planted six hybrid Populus deltoides clones belonging to the section Aigeiros (Aig), LL1, LL9, NL351, NL35, NL1388 and NL895, to three growth conditions in a greenhouse experiment, including low P, a high homogenous P supply and a high heterogeneous P supply. Functional traits, including foliar and root traits as well as rhizosphere processes, were measured. Large genotypic variation in shoot biomass and leaf P concentration was found in response to the P supply level and pattern. Compared with no P supply, LL1, LL9 and NL895 had a greater root length, biomass and P concentration in leaves under a homogenous P supply, while growth traits of NL351, NL35 and NL1388 were not significantly affected. A heterogeneous P supply enhanced the shoot biomass of LL1 and LL9. The root proliferation of LL1 and LL9 in P-rich patches was related to increased P acquisition in leaves. By contrast, a heterogeneous P supply did not enhance the biomass accumulation and the morphological plasticity of roots in other four genotypes, NL351, NL35, NL895 and NL1388, in P-rich patches. We found that functional traits or rhizosphere processes under low P could predict high P performance in Populus clones. Genotypes with a higher specific root length under low P can accumulate a larger biomass under a homogenous P supply. Conversely, high acid phosphatase concentrations decreased the positive impact of a heterogeneous P supply on a genotype's performance. Our results provide implications and applications for silviculture and forest management. [ABSTRACT FROM AUTHOR]