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Few studies have investigated the influence of water availability on plant population spatial patterns. We studied changes in the spatial patterns of Caragana stenophylla along a climatic drought gradient within the Inner Mongolian Plateau, China. We examined spatial patterns, seed density, "nurse effects" of shrubs on seedlings, transpiration rates and water use efficiency (WUE) of C. stenophylla across semi-arid, arid, and intensively arid zones. Our results showed that patches of C. stenophylla populations shifted from a random to a clumped spatial pattern towards drier environments. Seed density and seedling survival rate of C. stenophylla decreased from the semi-arid zone to the intensively arid zone. Across the three zones, there were more C. stenophylla seeds and seedlings underneath shrub canopies than outside shrub canopies; and in the intensively arid zone, there were almost no seeds or seedlings outside shrub canopies. Transpiration rates of outer-canopy leaves and WUE of both outer-canopy and inner-canopy leaves increased from the semi-arid zone to the intensively arid zone. In the intensively arid zone, transpiration rates and WUE of inner-canopy leaves were significantly lower and higher, respectively, than those of outer-canopy leaves. We conclude that, as drought stress increased, seed density decreased, seed proportions inside shrubs increased, and "nurse effects" of shrubs on seedlings became more important. These factors, combined with water-saving characteristics associated with clumped spatial patterns, are likely driving the changes in C. stenophylla spatial patterns.

Caraganaspecies are commonly distributed in desert regions. We hypothesized that the photosynthetic traits of desertCaraganaspecies could acclimated well to the desert environments, which are characterized by high temperature, intense radiation, and low moisture. To test our hypothesis, we studied the responses of photosynthesis to light, temperature and humidity, and fluorescence parameters of fourCaraganaspecies from desert region and oneCaraganaspecies from steppe region in Inner Mongolian Plateau. The desertCaraganaspecies had higher light compensation point, light saturation point, optimum temperature for photosynthesis, and lower optimum relative air humidity for photosynthesis than the steppeCaraganaspecies, and their net photosynthesis rates (Pn) were higher under high temperature, intense sunlight, and low humidity. The nonphotochemical quenching efficiency(NPQ)and minimal fluorescence(Fo)of the desertCaraganaspecies were higher, and the values of maximum fluorescence(Fm), maximum quantum yield(Fv/Fm), relative quantum yield (ΦPSII), and photochemical quenching coefficient (qP) were lower, except forC. korshinskii. The electron transport rate (ETR) of the desertCaraganaspecies was greater or similar to that ofC. microphylla.In summary, the photosynthetic traits of the desertCaraganaspecies acclimated well to desert environment, although such acclimation might be still not sufficient. The order of photosynthetic acclimation of the four species to desert environment is:C. korshinskii > C. stenophylla > C. tibetica > C. roborovskyi. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we examined the alterations in canopy size and reproduction of Caragana stenophylla along the climatic drought gradient on the Inner Mongolia Plateau, China. We found that the canopy area and height of C. stenophylla increased gradually with increase of drought stress from the semi-arid zone to the strongly arid zone. The proportions of sexual reproduction decreased and the asexual reproduction increased with increase of the climatic drought stress. The majority of C. stenophylla offspring grew (separately) outside shrubs in the semi-arid (63.9%) and the arid zones (45.8%). But in the strongly arid zone, C. stenophylla offspring only grew inside shrubs. With the increase of climatic drought stress the ramet radius increased, while the spacer length decreased. In both the semi-arid and arid zones, the spacer length was more than 2 times of the ramet radius. Thus, some spaces were kept between the crowns of ramets. On the other hand, the spacer length was less than 2 times of the ramet radius in the strongly arid zone, so that the crowns were closely intertwined. Our results demonstrate that with the increase of climatic drought stress and associated desertification, the reproduction of C. stenophylla changes from more sexual reproduction to more clonal propagation; offspring establishment strategy changes from having more outside-shrub offspring to having only inside-shrub offspring; the clonal architecture changes from guerrilla type to phalanx type. Alterations in the reproduction of C. stenophylla along the climatic drought gradient result due to an increase of its canopy size from the northeast to the southwest on the Inner Mongolia Plateau. [Copyright &y& Elsevier]