Zhouping Shangguan

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic water use efficiency (WUE(i)) of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material (delta(p)) is increased by the increase of drought intensity. The delta(p) at a given level of C(i)/C(a) is reduced by nitrogen deficiency. Leaf carbon isotope discrimination (Delta) is increased by the increase of nitrogen nutrition and decreased by the increase of drought intensity. Transpirational water use efficiency (WUE(t)) is negatively correlated with Delta in both nitrogen supply treatments and increased with the nitrogen supply.

Effects of Nitrogen Nutrition and Water Deficit on Net Photosynthetic Rate and Chlorophyll Fluorescence in Winter Wheat

Summary The responses of photosynthetic gas exchange and Chi fluorescence to nitrogen nutrition were studied under well-watered and drought conditions in winter wheat leaves. Nitrogen deficiency and water deficit strongly reduced the photosynthetic activity at light saturation level. For the well-watered treatment, the net photosynthetic rate was stimulated in the high-N (15 mmol/L N) plants as compared with the low-N (1.5 mmol/L N) plants and leaf conductance for water vapour was lower in the high-N than in the low-N treatment. As drought progressed, the net photosynthetic rate was significantly inhibited in the high-N plants as compared with the low-N plants. However, no significant nitrogen effect was noticed for net photosynthetic rate and leaf conductance for water vapour. The quantum yield of photochemical efficiency of PS II ( Fv/Fm ) determined on the youngest fully expanded leaf was unaffected by water stress, but it was lower for the low-N than for the high-N treatment. Nitrogen deficiency resulted in a decrease in the total Chi content and an inaease in the Chi a/b ratio; however, no difference was observed between the water treatments. During steady-state photosynthesis, the values of photochemical quenching decreased with increasing water stress in all treatments. For plants grown at low nitrogen nutrition photochemical quenching was higher than that for plants receiving high-N nutrition. The values of non-photochemical quenching decreased with increasing water stress in all treatments. Nitrogen deficiency and water stress decreased the efficiency of the PS II ( Fv/Fo ) and the efficiency of potential photosynthetic quantum conversion ( Fd/Fs ) of leaves significantly.

A model for regional optimal allocation of irrigation water resources under deficit irrigation and its applications

Abstract It is important to promote efficient use of water through better management of water resources, for social and economical sustainability in arid and semi-arid areas, under the conditions of severe water shortage. Based on the developments in deficit irrigation research, a recurrence control model for regional optimal allocation of irrigation water resources, aiming at overall maximum efficiency, is presented, with decomposition-harmonization principles of large systems. The model consists of three levels (layers). The first level involves dynamic programming (DP) for optimization of crop irrigation scheduling. The second level deals with optimal allocation of water resources among various crops. The last level concerns optimal allocation of water resources among different sub-regions. As a test, this model was applied to the combined optimal allocation of multiple water resources (surface, ground and in-take from the Weihe river) of Yangling, a semi-arid region on the Loess Plateau, China. Exemplary computation showed that not only are the results rational, but the method can also effectively overcome possible “dimensional obstacles” in dynamic programming of multiple dimensions. Furthermore, each sub-model is relatively independent by using various optimization methods. The model represents a new approach for improving irrigation efficiency, implementing water-saving irrigation, and solving the problem of water shortage in the region studied. The model can be extended in arid and semi-arid areas for better water management.

Interaction of Osmotic Adjustment and Photosynthesis in Winter Wheat Under Soil Drought

Summary The relationship between photosynthesis and osmotic adjustment in winter wheat ( Triticum aestivum L.) was studied in a controlled growth chamber under soil drought conditions. Leaf water potential, osmotic potential at full turgor, photosynthetic gas exchange, and chlorophyll fluorescence of plants under both control and stressed conditions were evaluated. Under a gradual drying process of soil water, the variability in the capacity of osmotic adjustment was observed, but not for a fast drying process of soil water. The plants that experienced the gradual drying process exhibited higher net photosynthetic gas exchange than those that experienced the fast drying process at a low water potential. Photosynthetic capacity of plants in the gradual drying process was greater than those in the fast drying process at low water potential. The data indicate that osmotic adjustment allows for maintenance of photosynthesis by stomatal adjustment and photosynthetic apparatus adjustment at low water potential.

“Grain for Green” driven land use change and carbon sequestration on the Loess Plateau, China

Land-use change is widely considered to be a major factor affecting soil carbon (C) sequestration (ΔCs). This paper studied changes to soil C stocks (Cs) following the conversion of farmland to forest, shrub and grassland across the key area for implementing Chinas “Grain for Green” — the Loess Plateau. The results are based on a synthesis of 44 recent publications (including 424 observations at 70 sites) which has allowed us to further refine our understanding of the mechanisms driving the increase in Cs following farmland conversion. This synthesis suggests that the ΔCs potential of the Loess Plateau could reach 0.59 Tg yr−1 based on an estimated annual average ΔCs rate of 0.29 Mg ha−1 yr−1. In the regions different rainfall zones both the main contributing factors and Cs dynamics varied. Across the entire Loess Plateau, Cs showed first an increasing (<5 yr) then a decreasing (6–10 yr) tendency only to increase (>10 yr) yet again. In addition, the ΔCs rates depended primarily on restoration age. This synthesis demonstrates that both the initial s Cs and the average annual temperature have a significant effect on ΔCs while the effect of land-use conversion type, rainfall zone, and average annual precipitation were minimal.

Soil desiccation occurrence and 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 arid soil layer is the ecological aftermath of intense soil desiccation due to disturbed plant succession and soil water reduction. The formation and types of arid 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 arid soil layer. Proper selection of vegetation types, adjusting tree density and other management practices can reduce the negative effects of the arid soil layer on forest vegetation.

Cytokinin-induced photosynthetic adaptability of Zea mays L. to drought stress associated with nitric oxide signal: Probed by ESR spectroscopy and fast OJIP fluorescence rise

Nitric oxide (NO), as a diffusible molecule, performs important roles in diverse physiological processes. Interestingly, NO signaling is based on interactions with plant hormones. The aim of this study was, first, to test the effect of cytokinin (CTK) on the primary reaction of photosynthesis under drought stress, and then to examine whether NO is involved in CTK-induced photosynthetic resistance due to its role as a second messenger in stress response. Under drought stress, plants were treated with CTK, or CTK plus the NO scavenger (Hemoglobin [Hb]) for 6h. The effects of CTK and Hb on fast OJIP fluorescence rise were then examined. At the same time, NO and reactive oxygen species (ROS) signals in all the treatments were detected by electron spin resonance (ESR) spectroscopy. The results showed that CTK-regulated fluorescence transient rise under drought stress and increased the electron donation capacity of photosynthesis system (PS) II. The plant photosynthetic performance index (PI) on an absorption basis and corresponding three PI components (RC/ABS, P(TR,) and P(ET)) also increased. High NO signal intensity alleviated drought-induced ROS damage to plants; thus, the signal probably played a direct role in eliciting CTK regulation to energy absorption (RC/ABS) and excitation energy trapped (P(TR)) in response to drought. Although CTK stimulated more excitation energy conversion to electron transfer (P(ET)), because NO was probably bound to the plastoquinone pool (PQ) of the electron transport chain, CTK decreased electron transport to the acceptor side of PSII (see V(I), Sm and N). Furthermore, CTK stimulated more NO signal formation, probably mainly via a nitrate reductase (NR) source under the conditions of the study, and Hb prevented stimulation from CTK. However, these results will require confirmation from future studies.

Changes in Soil Carbon and Nitrogen following Land Abandonment of Farmland on the Loess Plateau, China

The revegetation of abandoned farmland significantly influences soil organic C (SOC) and total N (TN). However, the dynamics of both soil OC and N storage following the abandonment of farmland are not well understood. To learn more about soil C and N storages dynamics 30 years after the conversion of farmland to grassland, we measured SOC and TN content in paired grassland and farmland sites in the Zhifanggou watershed on the Loess Plateau, China. The grassland sites were established on farmland abandoned for 1, 7, 13, 20, and 30 years. Top soil OC and TN were higher in older grassland, especially in the 0–5 cm soil depths; deeper soil OC and TN was lower in younger grasslands (<20 yr), and higher in older grasslands (30 yr). Soil OC and N storage (0–100 cm) was significantly lower in the younger grasslands (<20 yr), had increased in the older grasslands (30 yr), and at 30 years SOC had increased to pre-abandonment levels. For a thirty year period following abandonment the soil C/N value remained at 10. Our results indicate that soil C and TN were significantly and positively correlated, indicating that studies on the storage of soil OC and TN needs to focus on deeper soil and not be restricted to the uppermost (0–30 cm) soil levels.

Effect of nitrogen on root and shoot relations and gas exchange in winter wheat

The seedling growth of two drought-resistant wheat varieties was studied under solution culture in a plant growth chamber. The results showed that the shoot dry weight and leaf gas exchange parameters increased with the increase of nitrogen supply, but decreased when nitrogen supply reached a certain level. The optimum nitrogen concentrations for shoot dry weight and gas exchange were different among the varieties. The root growth was negatively correlated with the increase of nitrogen supply. The distribution of root length in different layers was similar for the two varieties. The root length was the longest at the layer of 5-15 cm, the shortest below 15 cm, and in between at the layer of 0-5 cm. The water use efficiency (WUE) decreased with increasing ratio of root to shoot (R/S), while leaf photosynthetic rate tended to increase initially and then decrease. The increase in R/S was unfavorable to increase WUE, and the appropriate R/S for leaf photosynthetic rate was about 0.5.

Ecological properties of soil water and effects on forest vegetation in the Loess Plateau

In the Loess Plateau of China, soil water has three ecological properties: high infiltration capacity, high storage capacity and availability to deep plant roots. Soil desiccation is the most serious problem for forest vegetation in the Loess Plateau. Arid soils are the result of intensified soil desiccation caused by disturbances in plant succession, which constitute the ecological foundation of soil water. The negative effects of the arid soil layer on surface water infiltration for recharging underground water are discussed in terms of ecological hydrology. The arid soil layer disrupts the link between surface water and underground water and prevents vertical precipitation infiltration from supplementing underground water. Forest vegetation has a significant runoff-retaining efficiency that reduces total runoff from forest areas leading to low surface and ground runoff which affect the water cycle on a watershed scale.