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In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (droughtadapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (A N ), stomatal conductance (g s ), substomatal CO 2 concentration (C i ), transpiration rate (E), actual photochemical efficiency of PSII (Φ PSII ), and maximum photochemical efficiency of PSII (F v /F m ) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (P r ), photosynthetic electron partitioning (J C /J T ), photochemical quenching coefficient (q P ), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (A N /E) was used as an indicator of water use efficiency (WUE). A N , apparent P r , Φ PSII , F v /F m , q P , and g s decreased, NPQ increased, and gross P r sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. C i in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low C i .

In semi‐arid areas of north‐west China, grain yields of wheat (Triticum aestivum L.) are higher in recently bred cultivars than those released six decades earlier. The gas exchange, chloroplast activity and yield of six spring wheat cultivars grown in the 1950s, Hst and Gs96 (early), in the 1970s, Gy602 and Dx24 (intermediate), and in the 1990s, Gc20 and Lc8275 (modern) were compared with adequate water (WET) and drought stress (DRY) to determine the effects of drought stress among the cultivars. The results showed that in the WET treatment, the modern cultivars had significantly higher rates of leaf gas exchange, photosystem 2 (PS2) maximal photochemical efficiency, actual quantum yield of PS2 (ФPS2), photochemical quenching of chlorophyll (qp) and lower non‐photochemical quenching (NPQ) than early cultivars, but had significantly lower gas exchange rates, intercellular CO2 concentration, ФPS2, qp and NPQ in the DRY treatment. In the WET treatment, the grain yield of early cultivars was significantly lower (10 %) than intermediate cultivars, but was significantly higher (17 %) than intermediate cultivars in the DRY treatment. The modern and intermediate cultivars had more sensitive stomata to water shortage, but the decreased activity of the PS2 reaction centre helped avoid damage from photoinhibition in these cultivars.

Abstract. Soil organic carbon (SOC) plays a vital role as both a sink for and source of atmospheric carbon. Revegetation of degraded arable land in China is expected to increase soil carbon sequestration, but the role of perennial legumes on soil carbon stocks in semiarid areas has not been quantified. In this study, we assessed the effect of alfalfa (Medicago sativa L.) and two locally adapted forage legumes, bush clover (Lespedeza davurica S.) and milk vetch (Astragalus adsurgens Pall.) on the SOC concentration and SOC stock accumulated annually over a 2 m soil profile. The results showed that the concentration of SOC in the bare soil decreased slightly over the 7 years, while 7 years of legume growth substantially increased the concentration of SOC over the 0-2.0 m soil depth. Over the 7-year growth period the SOC stocks increased by 24.1, 19.9 and 14.6 Mg C ha −1 under the alfalfa, bush clover and milk vetch stands, respectively, and decreased by 4.2 Mg C ha −1 in the bare soil. The sequestration of SOC in the 1-2 m depth of the soil accounted for 79, 68 and 74 % of the SOC sequestered in the 2 m deep soil profile under alfalfa, bush clover and milk vetch, respectively. Conversion of arable land to perennial legume pasture resulted in a significant increase in SOC, particularly at soil depths below 1 m.

Perennial forage legumes, particularly lucerne (Medicago sativa L.), play a significant role in crop/livestock mixed farming systems in the semiarid region of the Loess Plateau of China as stock feed and a source of nitrogen for subsequent crops. However, there is evidence that lucerne reduces soil water deep in the soil profile, thereby reducing subsequent crop productivity. From 2004 to 2010, this study evaluated the forage productivity and water use of two locally adapted perennial legume species, milk vetch (Astragalus adsurgens Pall.) and bush clover (Lespedeza davurica S.), compared with lucerne. The 7-year total and average annual forage yield of milk vetch were 56 and 8 t ha À1 and bush clover was 42 and 6 t ha À1 , respectively, significantly lower than lucerne at 91 and 13 t ha À1 . However, despite lower water-use efficiencies (16 and 12 kg ha À1 mm À1 for milk vetch and bush clover, respectively, compared to 22 kg ha À1 mm À1 for lucerne), the total 7-year water use in milk vetch and bush clover was 3500 mm and 3490 mm, respectively, which was 135-140 mm less than lucerne. After 7 years, lucerne had extracted water from the upper 5 m soil, whereas bush clover used water mainly from the upper 2 m of the soil profile and milk vetch still had some water available below 3 m. We conclude that while the locally adapted for-age legumes were not as productive as lucerne as a source of fodder in mixed cropping/livestock system in this region, they use less water, which may be advantageous in drier regions.

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