Weikai Bao

Effects of water stress and nitrogen supply on leaf gas exchange and fluorescence parameters of Sophora davidii seedlings

Two-month-old seedlings of Sophora davidii were subjected to a randomized complete block design with three water (80, 40, and 20 % of water field capacity, i.e. FC80, FC40, and FC20) and three N supply [N0: 0, Nl: 92 and Nh: 184 mg(N) kg−1(soil)] regimes. Water stress produced decreased leaf area (LA) and photosynthetic pigment contents, inhibited photosynthetic efficiency, and induced photodamage in photosystem 2 (PS2), but increased specific leaf area (SLA). The decreased net photosynthetic rate (PN) under medium water stress (FC40) compared to control (FC80) might result from stomatal limitations, but the decreased PN under severe water deficit (FC20) might be attributed to non-stomatal limitations. On the other hand, N supply could improve photosynthetic capacity by increasing LA and photosynthetic pigment contents, and enhancing photosynthetic efficiency under water deficit. Moreover, N supply did a little in alleviating photodamages to PS2 caused by water stress. Hence water stress was the primary limitation in photosynthetic processes of S. davidii seedlings, while the photosynthetic characters of seedlings exhibited positive responses to N supply. Appropriate N supply is recommended to improve photosynthetic efficiency and alleviate photodamage under water stress.

Growth, biomass partitioning, and water-use efficiency of a leguminous shrub (Bauhinia faberi var. microphylla) in response to various water availabilities

Responses of the endemic leguminous shrub Bauhinia faberi var. microphylla, to various soil water supply regimes were studied in order to assess water stress tolerance of seedlings. Two-month-old seedlings were grown under water supply regimes of 100, 80, 60, 40, and 20% water field capacity (FC), respectively, in a temperature and light-controlled greenhouse. Plant height and leaf number were measured monthly over a 4-month period, while water use (WU), water-use efficiency (WUE), leaf relative water content (RWC), biomass production and its partitioning were recorded at the end of the experiment. Seedlings exhibited the greatest biomass production, height, basal diameter, branch number, leaf number, and leaf area when soil content was at 100% FC, and slightly declined at 80% FC. These parameters declined significantly under 60% FC water supply, and severely reduced under 40 and 20% FC. RWC, WU and WUE decreased, while the ratio of root mass to stem mass (R:S) increased in response to decreasing water supply. Water stress caused leaf shedding, but not plant death. The results demonstrated that B. faberi var. microphylla seedlings could tolerate drought by reducing branching and leaf area while maintaining a high R:S ratio. However, low dry mass and WUE at 40 and 20% FC suggested that the seedlings did not produce significant biomass under prolonged severe water deficit. Therefore, before introducing B. faberi var. microphylla in vegetation restoration efforts, water supply above 40% FC is recommended for seedlings to maintain growth.

Leaf Growth, Gas Exchange and Chlorophyll Fluorescence Parameters in Response to Different Water Deficits in Wheat Cultivars

Abstract We investigated responses of wet climate (CY17) and dry climate (XN889) Trititcum aestivum L cultivars under 85, 55 and 25% field water capacity (FC). Less decrease in grain yield, relative water content, growth, gas exchange and chlorophyll fluorescence parameters indicated that XN889 was more drought-tolerant than CY17. At 55%FC, CY17 showed a lower net photosynthetic rate (Pn) than XN889 mainly due to stomatal closure. Stomatal closure was also observed in XN889, but its Pn was higher at 55%FC than at 85%FC. The higher Pn in XN889 may be associated with a higher chlorophyll content and resulting increase in photochemical quenching (qP), apparent electron transport rate, and effective quantum yield of photosystem II (PSII). Both cultivars showed photodamage at 25%FC, but XN889 showed less photodamage in terms of maximal PSII photochemical efficiency. XN889 showed higher qP and non-photochemical quenching than CY17, further demonstrating its superior drought tolerance.

Evaluation of Soil Fertility Under Different Cupressus chengiana Forests Using Multivariate Approach

The distribution and growing conditions of Cupressus chengiana forests along with the physical and chemical properties of soils in Northwest Sichuan were studied in 2002 to investigate the conditions and characteristics of soil fertility of C. chengiana and to compare and investigate differences of soil fertility for six C. chengiana populations and their relationships with vegetation, climate and disturbance. The results of the study at 0-20 cm soil depth showed that 1) significant differences (P < 0.05) existed among populations for soil bulk density, soil total porosity, capillary porosity, maximum water-holding capacity, capillary water-holding capacity and topsoil natural water content; 2) chemical characteristics of soil organic matter, total N, total P, alkali-hydrolyzable N, available P, available K and cation exchange capacity were significantly different among the populations; and 3) based on the significant effect of soil fertility factors on forest growth, soil physical and chemical characteristics could be selected as an integrated fertility index (IFI) for evaluation of different C. chengiana populations. Principal component and cluster analyses showed significant differences probably due to the difference of vegetation conditions, management measurements, human-induced disturbances and environmental factors. In order to protect the soil ecological functions in fragile ecological regions, C. chengiana could be used in programs enclosing the hill for natural afforestation, natural forest protection programs, and programs replacing agriculture with afforestation measures.

Shrub island effects on a high-altitude forest cutover in the eastern Tibetan Plateau

Abstract• ContextThe roles of woody-plant islands are well documented in low-altitude regions, but research related to such shrub effects in high-altitude regions is scant.• AimsFour common shrub species (Cerasus trichostoma, Ribes glaciale, Rosa omeiensis and Salix sphaeronymphe) in a high-altitude forest cutover of the eastern Tibetan Plateau, were chosen to evaluate the effects of both species and size of shrub islands on microhabitats, herbaceous communities and woody seedling regeneration.• MethodsTotal 86 shrubs with different sizes were investigated; The shrub size, herb community structure and species composition, litter, soil nutrient and microclimate parameters beneath the shrub canopies were also measured.• ResultsAll shrubs significantly ameliorated microclimates, increased content of soil organic matter and total nitrogen, both grass and forb species richness, and litter cover and biomass, and promoted woody seedling recruitment (richness and number), but decreased cover and biomass of the herbaceous community beneath them. These effects were greater for larger shrubs, and also varied among shrub species with different crown architectures. We also found differences in species-dependency of the shrub effect for the responses of the herbaceous and woody seedling species, suggesting that shrubs also indirectly facilitate forbs and seedling regeneration through competition release of grasses. We conclude that shrub-island effects are size- and species-dependent. In order to accelerate natural succession and restoration in alpine cutovers, shrub island preservation and their effective utilization as reforestation microhabitats should be integrated into vegetation management procedures.

Statistical Analysis of Leaf Water Use Efficiency and Physiology Traits of Winter Wheat Under Drought Condition

Five statistical methods including simple correlation, multiple linear regression, stepwise regression, principal components, and path analysis were used to explore the relationship between leaf water use efficiency (WUE) and physiological traits (photosynthesis rate, stomatal conductance, transpiration rate, intercellular CO2 concentration, etc.) of 29 wheat cultivars. The results showed that photosynthesis rate, stomatal conductance, and transpiration rate were the most important leaf WUE parameters under drought condition. Based on the results of statistical analyses, principal component analysis could be the most suitable method to ascertain the relationship between leaf WUE and relative physiological traits. It is reasonable to assume that high leaf WUE wheat could be obtained by selecting breeding materials with high photosynthesis rate, low transpiration rate, and stomatal conductance under dry area.

New insights into leaf and fine-root trait relationships: implications of resource acquisition among 23 xerophytic woody species

Abstract Functional traits of leaves and fine root vary broadly among different species, but little is known about how these interspecific variations are coordinated between the two organs. This study aims to determine the interspecific relationships between corresponding leaf and fine‐root traits to better understand plant strategies of resource acquisition. SLA (Specific leaf area), SRL (specific root length), mass‐based N (nitrogen) and P (phosphorus) concentrations of leaves and fine roots, root system, and plant sizes were measured in 23 woody species grown together in a common garden setting. SLA and SRL exhibited a strong negative relationship. There were no significant relationships between corresponding leaf and fine‐root nutrient concentrations. The interspecific variations in plant height and biomass were tightly correlated with root system size characteristics, including root depth and total root length. These results demonstrate a coordinated plant size‐dependent variation between shoots and roots, but for efficiency, plant resource acquisition appears to be uncoupled between the leaves and fine roots. The different patterns of leaf and fine‐root traits suggest different strategies for resource acquisition between the two organs. This provides insights into the linkage between above‐ and belowground subsystems in carbon and nutrient economy.

Does thinning‐induced gap size result in altered soil microbial community in pine plantation in eastern Tibetan Plateau?

Abstract Although the effects of gap formation resulting from thinning on microclimate, plant generation and understory plant community have been well documented, the impact of thinning on soil microbial community and related ecological functions of forests particularly in subalpine coniferous region is largely unknown. Here, the effects of thinning on soil microbial abundance and community structure using phospholipid fatty acid (PLFA) in pine plantations were investigated 6 years after thinning. The experimental treatments consisted of two distinct‐sized gaps (30 m2 or 80 m2 in size) resulting from thinning, with closed canopy (free of thinning) as control. Soil temperature as well as the biomass of actinomycete and unspecific bacteria was sensitive to gap formation, but all these variables were only responsive to medium gap. Nonmetric multidimensional scaling confirmed that soil microbial community was responsive to gap size. In addition, gap size exerted contrasting effect on bacteria‐feeding nematode and fungi‐feeding nematodes. In conclusion, thinning‐induced gap size would affect soil microbial community through changing soil temperature or the abundance of fungi‐feeding nematodes.

Higher photosynthetic capacity and different functional trait scaling relationships in erect bryophytes compared with prostrate species

Ecophysiological studies of bryophytes have generally been conducted at the shoot or canopy scale. However, their growth forms are diverse, and knowledge of whether bryophytes with different shoot structures have different functional trait levels and scaling relationships is limited. We collected 27 bryophyte species and categorised them into two groups based on their growth forms: erect and prostrate species. Twenty-one morphological, nutrient and photosynthetic traits were quantified. Trait levels and bivariate trait scaling relationships across species were compared between the two groups. The two groups had similar mean values for shoot mass per area (SMA), light saturation point and mass-based nitrogen (Nmass) and phosphorus concentrations. Erect bryophytes possessed higher values for mass-based chlorophyll concentration (Chlmass), light-saturated assimilation rate (Amass) and photosynthetic nitrogen/phosphorus use efficiency. Nmass, Chlmass and Amass were positively related, and these traits were negatively associated with SMA. Furthermore, the slope of the regression of Nmass versus Chlmass was steeper for erect bryophytes than that for prostrate bryophytes, whereas this pattern was reversed for the relationship between Chlmass and Amass. In conclusion, erect bryophytes possess higher photosynthetic capacities than prostrate species. Furthermore, erect bryophytes invest more nitrogen in chloroplast pigments to improve their light-harvesting ability, while the structure of prostrate species permits more efficient light capture. This study confirms the effect of growth form on the functional trait levels and scaling relationships of bryophytes. It also suggests that bryophytes could be good models for investigating the carbon economy and nutrient allocation of plants at the shoot rather than the leaf scale.

Appropriate nitrogen supply could improve soil microbial and chemical characteristics with Sophora davidii seedlings cultivated in water stress conditions

Abstract A greenhouse experiment was conducted to investigate the changes of soil microbial activities and chemical properties under different water and nitrogen (N) supply conditions. A completely randomized design was subjected to three water regimes (80%, 40% and 20% water field capacity (FC)) and three N supply regimes (control, N0: 0 mg N kg−1 soil; low N supply, Nl: 92 mg N kg−1 soil; and high N supply, Nh: 184 mg N kg−1 soil) by potting with 2-month-old Sophora davidii seedlings. Water stress decreased the content of soil organic carbon (C), available N and phosphorus (P), the ratio of C/N, the ratio of C/P, as well as activities of soil invertase, urease and alkaline phosphatase, but not reduced microbial biomass C, N and P contents. Soil microbial and chemical characteristics also exhibited strong responses to N supply, and these responses were inconsistent among N supply levels. The contents of soil organic C and available P showed stronger positive responses to Nl than to Nh, while the available N content increased with increasing N supply. Additionally, Nl rather than the other two N treatments led to increased microbial biomass N and invertase activity under 20% FC treatment, even though the invertase activity increased in Nh treatment under 40% FC and 80% FC treatments. Nl treatment also increased the C/P ratio and alkaline phosphatase activity. These results suggest that water and N co-limited nutrient mineralization and microbial activity, and that these characteristics responded positively to Nl. Therefore, appropriate or low N supply is recommended to increase soil quality restrained by water stress, thereby facilitating S. davidii seedling establishment under water deficit conditions.