Water adaptive traits of deep-rooted C_3 halophyte(Karelinia caspica(Pall.) Less.) and shallow-rooted C_4 halophyte(Atriplex tatarica L.) in an arid region,Northwest China

This paper focused on the water relations of two halophytes differing in photosynthetic pathway, phe- notype, and life cycle： Karelinia caspica （Pall.） Less. （C3, deep-rooted perennial Asteraceae grass） and Atriplex tatarica L. （C4, shallow-rooted annual Chenopodiaceae grass）. Gas exchange, leaf water potential, and growth characteristics were investigated in two growing seasons in an arid area of Xinjiang to explore the physiological adaptability of the two halophytes. Both K. caspica and A. tatarica showed midday depression of transpiration, in- dicating that they were strong xerophytes and weak midday depression types. The roots of A. tatarica were con- centrated mainly in the 0-60 cm soil layer, and the leaf water potential （~L） increased sharply in the 0-20 cm layer due to high soil water content, suggesting that the upper soil was the main water source. On the other hand, K. caspica had a rooting depth of about 1.5 m and a larger root/shoot ratio, which confirmed that this species uptakes water mainly from deeper soil layer. Although A. tatarica had lower transpiration water consumption, higher water use efficiency （WUE）, and less water demand at the same leaf water potential, it showed larger water stress impact than K. caspica, indicating that the growth of A. tatarica was restricted more than that of K. caspica when there was no rainfall recharge. As a shallow-rooted C4 species, A. tatarica displayed lower stomatal conductance, which could to some extent reduce transpiration water loss and maintain leaf water potential steadily. In contrast, the deep-rooted C3 species K. caspica had a larger root/shoot ratio that was in favor of exploiting groundwater. We concluded that C3 species （K. caspica） tapes water and C4 species （A. tatarica） reduces water loss to survive in the arid and saline conditions. The results provided a case for the phenotype theory of Schwinning and Ehleringer on halophytic plants.

Effects of fertigation scheme on N uptake and N use efficiency in cotton

While fertigation can increase fertilizer use efficiency, there is an uncertainly as to whether the fertilizer should be introduced at the beginning of the irrigation or at the end, or introduced during irrigation. Our objective was to determine the effect of different fertigation schemes on nitrogen (N) uptake and N use efficiency (NUE) in cotton plants. A pot experiment was conducted under greenhouse conditions in year 2004 and 2005. According to the application timing of nitrogen (N) fertilizer solution and water (W) involved in an irrigation cycle, four nitrogen fertigation schemes [nitrogen applied at the beginning of the irrigation cycle (N-W), nitrogen applied at the end of the irrigation cycle (W-N), nitrogen applied in the middle of the irrigation cycle (W-N-W) and nitrogen applied throughout the irrigation cycle (N&W)] were employed in a completely randomized design with four replications. Cotton was grown in plastic containers with a volume of 84 l, which were filled with a clay loam soil and fertilized with 6.4 g of N per pot as unlabeled and 15N-labeled urea for 2004 and 2005, respectively. Plant total dry matter (DM) and N content in N-W was significantly higher than in N&W in both seasons, but these were not consistent for W-N and W-N-W treatments. In year 2005, a significantly higher nitrogen derived from fertilizer (NDFF) for the whole plant was found in W-N and N-W than that in W-N-W and N&W. Fertigation scheme had a consistent effect on total NUE: N-W had the highest NUE for the whole plant, but this was not significantly different from W-N. Treatments W-N and W-N-W had similar total NUE, and N&W had the lowest total NUE. After harvesting, the total residual fertilizer N in the soil was highest in W-N, lowest in N-W, but this was not significantly different from N&W and W-N-W treatments. Total residual NO3-N in the soil in N&W and W-N treatments was 20.7 and 21.2% higher than that in N W, respectively. The total 15 N recovery was not statistically significant between the four fertigation schemes. In this study, the fertigation scheme N-W (nitrogen applied at the beginning of an irrigation cycle) increased DM accumulation, N uptake and NUE of cotton. This study indicates that Nitrogen application at the beginning of an irrigation cycle has an advantage on N uptake and NUE of cotton. Therefore, NUE could be enhanced by optimizing fertilization schemes with drip irrigation.

K^(+)and Na^(+)fluxes in roots of two Chinese Iris populations

Maintenance of ion homeostasis,particularly the regulation of K^(+)and Na^(+)uptake,is important for all plants to adapt to salinity.Observations on ionic response to salinity and net fluxes of K^(+),Na^(+)in the root exhibited by plants during salt stress have highlighted the need for further investigation.The objectives of this study were to compare salt adaptation of two Chinese Iris(Iris lactea Pall.var.chinensis(Fisch.)Koidz.)populations,and to improve understanding of adaptation to salinity exhibited by plants.Plants used in this study were grown from seeds collected in the Xinjiang Uygur Autonomous Region(Xj)and Beijing Municipality(Bj),China.Hydroponicallygrown seedlings of the two populations were supplied with nutrient solutions containing 0.1(control)and 140 mmol·L^(–1) NaCl.After 12 days,plants were harvested for determination of relative growth rate and K^(+),Na^(+)concentrations.Net fluxes of K^(+),Na^(+)from the apex and along the root axis to 10.8 mm were measured using noninvasive micro-test technique.With 140 mmol·L^(–1) NaCl treatment,shoots for population Xj had larger relative growth rate and higher K^(+)concentration than shoots for population Bj.However,the Na^(+)concentrations in both shoots and roots were lower for Xj than those for Bj.There was a lower net efflux of K^(+)found in population Xj than by Bj in the mature zone(approximately 2.4^(–1)0.8 mm from root tip).However,no difference in the efflux of Na^(+)between the populations was obtained.Population Xj of I.lactea continued to grow normally under NaCl stress,and maintained a higher K^(+)/Na^(+)ratio in the shoots.These traits,which were associated with lower K^(+)leakage,help population Xj adapt to saline environments.