Effects of Soil Water and Nitrogen on Growth and Photosynthetic Response of Manchurian Ash (Fraxinus mandshurica) Seedlings in Northeastern China

Soil water and nitrogen (N) are considered to be the main environmental factors limiting plant growth and photosynthetic capacity. However, less is known about the interactive effects of soil water and N on tree growth and photosynthetic response in the temperate ecosystem. seedlings. The seedlings were exposed to three water regimes including natural precipitation (CK), higher precipitation (HW) (CK +30%) and lower precipitation (LW) (CK −30%), and both with and without N addition for two growing seasons. We demonstrated that water and N supply led to a significant increase in the growth and biomass production of the seedlings. LW treatment significantly decreased biomass production and leaf N content, but they showed marked increases in N addition. N addition could enhance the photosynthetic capability under HW and CK conditions. Leaf chlorophyll content and the initial activity of Rubisco were dramatically increased by N addition regardless of soil water condition. The positive relationships were found between photosynthetic capacity, leaf N content, and SLA in response to water and N supply in the seedling. Rubisco expression was up-regulated by N addition with decreasing soil water content. Immunofluorescent staining showed that the labeling for Rubisco was relatively low in leaves of the seedlings under LW condition. The accumulation of Rubisco was increased in leaf tissues of LW by N addition. seedlings, which may provide novel insights on the potential responses of the forest ecosystem to climate change associated with increasing N deposition

Stable Isotope Biogeochemistry of Seabird Guano Fertilization: Results from Growth Chamber Studies with Maize (Zea Mays)

Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ(15)N). Animal excrement is known to impact plant δ(15)N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.This paper presents isotopic (δ(13)C and δ(15)N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of (15)N enrichment in fertilized plants is very large, with δ(15)N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ(15)N values ranged between -0.3 and 5.7‰. Intraplant and temporal variability in δ(15)N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ(13)C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.The results presented in this study demonstrate the very large impact of seabird guano on maize δ(15)N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material

Relationship between delta C-13 and photosynthetic parameters and their responses to leaf nitrogen content in six broadleaf tree species

Stable carbon isotope composition (delta(13)C), net photosynthetic rate (P-N), actual quantum yield of photosystem 2 (PS2) electron transport (Phi(PS2)), nitrogen content (N-c), and photosynthetic nitrogen use efficiency (PNUE) in the leaves of six broadleaf tree species were determined under field environmental conditions. The six tree species were Magnolia liliflora Desr., M. grandiflora Linn., M. denudata Desr., Prunus mume (Sieb.) Sieb. et Zucc. cv. Meiren Men, P. mume (Sieb.) Sieb. et Zucc. f. alphandii (Carr.) Rehd., and P. persica (L.) Batsch. var. rubro-plena. The relationships among delta(13)C, Phi(PS2) P-N, and PNUE, as well as their responses to N-c in the six species were also studied. Both P-N and delta(13)C negatively correlated with N-c, but Phi(PS2) positively correlated with N-c. This indicated that with N-c increase, P-N and delta(13)C decreased, while Phi(PS2) increased. There were weak negative correlations between delta(13)C and PNUE, and strong negative correlations (p < 0.01) between Phi(PS2) and PNUE. According to the variance analysis of parameters, there existed significant interspecific differences (p < 0.001) of delta(13)C, P-N, Phi(PS2), PNUE, and N-c among the tree seedlings of the six tree species, which suggests that the potential photosynthetic capacities depend on plant species, irradiance, and water use capacity under field conditions

Soil desiccation occurrence an its impact on forest vegetation in the Loess Plateau of China

Soil desiccation is a major issue limiting development and sustainability of forest vegetation in the Loess Plateau of China. Better understanding of the mechanisms of soil desiccation in the Loess Plateau can help scientists and forest managers improve vegetation management practices. The and soil layer is the ecological aftermath of intense soil desiccation due to disturbed plant succession and soil water reduction. The formation and types of and soil layer in the Loess Plateau were investigated to determine major causes of soil desiccation and its impact on forest vegetation. The negative effects of soil desiccation on the ecological environment and forest vegetation mainly include drying microclimate, degrading soil quality, poor vegetation growth, difficult forest renewal from natural seed banks, making it even more difficult to reforest forest lands and grasslands following plant senescence. Low precipitation, high evaporation, soil and water losses, improper selection of vegetation types, and too high population density of trees are probably the major reasons for the and soil layer. Proper selection of vegetation types, adjusting tree density and other management practices can reduce the negative effects of the and soil layer on forest vegetation

Spatial patterns of photosynthetic characteristics and leaf physical traits of plants in the Loess Plateau of China

The spatial patterns of photosynthetic characteristics and leaf physical traits of 171 plants belonging to nine life-forms or functional groups (trees, shrubs, herbs, evergreen trees, deciduous trees, C-3 and C-4 herbaceous plants, leguminous and non-leguminous species) and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, ranging from south to north in the Loess Plateau of China were studied. The results showed that the leaf light-saturated photosynthetic rate (P-max), photosynthetic nitrogen use efficiency (PNUE), chlorophyll content (Chl), and leaf mass per area (LMA) of all the plants in the Loess Plateau varied significantly among three life-form groups, i.e., trees, shrubs and herbs, and two groups, i.e., evergreen trees and deciduous trees, but leaf nitrogen content differed little among different life-form groups. For the 171 plants in the Loess Plateau, leaf P-max was positively correlated with PNUE. The leaf nitrogen content per unit area (N-area) was positively correlated but Chl was negatively correlated with the LMA. When controlling the LMA, the N-area was positively correlated with the Chl (partial r = 0.20, P < 0.05). With regard to relationships between photosynthetic characteristics and leaf physical traits, the P-max was positively correlated with N (area), while the PNUE was positively correlated with the Chl and negatively correlated with the N-area and LMA. For all the species in the Loess Plateau, the PNUE was negatively correlated with the latitude and annual solar radiation (ASR), but positively correlated with the mean annual rainfall (MAR) and mean annual temperature (MAT). With regard to the leaf physical traits, the leaf Chl was negatively correlated with the latitude and ASR, but positively correlated with the MAR and MAT. However, the N-area and LMA were positively correlated with the latitude and ASR, but negatively correlated with the MAR and MAT. In general, leaf N-area and LMA increased, while PNUE and Chl decreased with increases in the latitude and ASR and decreases in MAR and MAT

Vertical distribution of fine roots in relation to soil factors in Pinus tabulaeformis Carr. forest of the Loess Plateau of China

Growth and vertical distribution of fine root closely depend on soil resource availability. Better understanding of relationships of root profile with vertical distribution of available soil resource and soil characteristics can allow ecologists to predict the fine root distribution on the scales ranging from individual plants to vegetation communities. The objective of the study was to understand the fine root mass density (FRMD), fine root length density (FRLD), fine root area density (FRAD), mean root diameter and specific root length (SRL), vertical distribution in soil profile and their relation with soil environment factors in semiarid and arid Loess Plateau of China. The vertical fine root distribution and soil bulk density, soil moisture and soil inorganic N in 0-60 cm soil profile (0-15, 15-30, 30-45 and 45-60 cm intervals) were investigated by soil coring methods in three Pinus tabulaeformis Carr. forests chosen at three locations. The fine root density parameters (FRMD, FRLD and FRAD) and SRL peaked in the most upper soil layer (0-15 cm interval) and decreased with increased soil depth. The results provided a strong support that soil water rather than soil inorganic N is a key control on fine root distribution in the Loess Plateau. With increased soil moisture, the root mass, length and SRL increased and the mean root diameter decreased. The effects of soil bulk density on the fine root parameters were consistent with those of the soil water. An unexpected result was obtained about the relationships between soil organic N and the root distributions and occurrences because of no differences among the soil depth intervals in soil inorganic N content. It might be associated with severe soil water deficit limiting soil nitrogen utilization efficiency in arid Loess Plateau

The effects of ryegrass roots and shoots on loess erosion under simulated rainfall

Numerous studies have demonstrated that vegetation coverage is very important to control soil erosion by water. However, the combined impacts of plant roots and shoots on soil erosion by water and the relative contributions of the roots and shoots are not clearly understood. Four rainfall simulation experiments with the rainfall intensity at 1.5 mm min(-1) were conducted at an interval of 5 weeks to investigate the effects of ryegrass (Lolium perenne L.) shoots and roots on soil erosion and runoff reductions. Ten ryegrass planted pans and four fallow pans were prepared for the experiments. The first rainfall simulation experiment was conducted after ryegrass had been planted for 12 weeks. It showed that compared with the runoffs in the fallow pans, the runoff in the planted pans decreased 25% and 70% in the 12th week and the 27th week, respectively; and the sediment decrements amounted up to 95% in the 27th week. The results also indicated that the shoot effect on runoff reduction, accounting for over 50% except in the 27th week when the shoot affect also accounted for 44%, was relatively greater than the root effect. However, the roots contributed more to soil loss reduction than the shoots, and in particular accounted for 90% of soil loss reduction at the 27th week. Both the soil erosion rate and average infiltration rate were linearly correlated with root surface area density in cm(2) root surface area per unit soil volume. Ryegrass planting could improve soil physical properties, especially soil aggregate stability, which increased from 33.1% in the 12th week to 38.5% in the 27th week. The study results are probably useful in evaluating the effects of plant shoots and roots on soil erosion control. (c) 2006 Elsevier B.V. All rights reserved