Drought induced changes in growth, leaf gas exchange and biomass production in Albizia lebbeck and Cassia siamea seedlings.

Diurnal trends in net photosynthesis rate (P(N)), stomatal conductance (g(s)), water use efficiency (WUE) and biomass were compared in six-month-old seedlings of Albizia lebbeck and Cassia siamea, under different levels of drought stress. The potted plants were subjected to four varying drought treatment by withholding watering for 7 (D1), 14(D2) and 25 (D3) days. The fourth group (C) was watered daily and treated as unstressed (control). Species differed significantly (p < 0.001) in their physiological performance under varying stress conditions. Higher P(N) of 11.6 +/- 0.05 in control followed by 4.35 +/- 0.4 in D1 and 2.83 +/- 0.18 micromol m(-2) s(-1) in D2 was observed in A. lebbeck. A significant (p < 0.001) reduction in P(N) was observed in C. siamea (C 7.65 +/- 0.5 micromol m(-2) s(-1), D1, 2.56 +/- 0.33 micromol m(-2) s(-1) and D2, 1.4 +/- 0.01 micromol m(-2) s(-1)) at 9 hr. A positive correlation was seen between P(N) and g(s) (A. lebbeck, r2 = 0.84; C. siamea, r2 = 0.82). Higher WUE was observed in C. siamea (D2, 7.1 +/- 0.18 micromol m(-2) s(-1); D3, 8.39 +/- 0.11 micromol m(-2) s(-1)) than A. lebbeck, (control, 7.58 +/- 0.3 micromol m(-2) s(-1) and D3, 8.12 +/- 0.15 micromol m(-2) s(-1)). The chlorophyll and relative water content (RWC) was more in A. lebbeck than C. siamea. Maximum biomass was produced by A. lebbeckthan C. siamea. From the study, one could conclude that A. lebbeckis better than C. siamea in adopting suitable resource management strategy and be best suited for the plantation programs in the semi-arid dry lands.

[Determination of physiological indices in Albizzia julibrissin Durazz seedlings under alkaline stress with visible spectrophotometry].

There is a large area of saline-alkali soil in our country, and soil alkalization is always a problem affecting urban gardening. To examine the capacity of alkaline resistance of Albizzia julibrissin Durazz seedlings, the contents of MDA, soluble sugar and proline, and the activity of POD and SOD in Albizzia julibrissin durazz tree body were measured by means of visible spectrophotometry. Also, the change patterns of the five indexes with different treatment concentration and time were analyzed. Attempts were then made to elucidate the physiological mechanism of how alkaline stress affects the growth of the Albizzia julibrissin durazz tree, which could provide theoretical foundation for planting and gardening and an approach to dealing with the difficulties in planting and gardening in saline and alkaline area. The results showed that with the increase in Na2 CO3 concentration, the contents of MDA and soluble sugar in the leaves slowly ascended when the treatment concentration was lower than 75 mmol x L(-1), and then rapidly increased when the treatment concentration was higher than 75 mmol x L(-1); There were significant differences between different treatments. Proline content exhibited the same change pattern with MDA and soluble sugar. It slowly ascended when the treatment concentration was lower than 100 mmol x L(-1), whereas it sharply increased when the treatment concentration was above 100 mmol x L(-1); The changes in SOD and POD were similar, showing a unimodal pattern. However, the treatment concentration corresponding to the maximum of SOD and POD was 50 and 75 mmol x L(-1), respectively. With the changes in stress time, in addition, the contents of MDA treated with the same concentration increased gradually. However, praline, soluble sugar, SOD and POD changed irregularly. These results indicated that Albizzia julibrissin Durazz could resist the alkaline stress by modulating values of physical indexes such as the contents of MDA, soluble sugar and proline and the activity of POD and SOD.

A multiyear estimate of the effective pollen donor pool for Albizia julibrissin.

Studies of pollen movement in plant populations are often limited to a single reproductive event, despite concerns about the adequacy of single-year measures for perennial organisms. In this study, we estimate the effective number of pollen donors per tree from a multiyear study of Albizia julibrissin Durazz (mimosa, Fabaceae), an outcrossing, insect-pollinated tree. We determined 40 seedling genotypes for each of 15 seed trees during 4 successive years. A molecular analysis of variance of the pollen gametes fertilizing the sampled seeds was used to partition variation in pollen pools among seed trees, among years, and within single tree-year collections. Using these variance components, we demonstrate significant male gametic variability among years for individual trees. However, results indicate that yearly variation in the 'global pollen pool', averaged over all 15 seed trees for these 4 years, is effectively zero. We estimate the effective number of pollen donors for a single mimosa tree (N(ep)) to be 2.87. Single season analyses yield N(ep) approximately 2.05, which is 40% less than the value of N(ep) estimated from 4 years of data. We discuss optimal sampling for future studies designed to estimate N(ep). Studies should include more trees, each sampled over at least a few years, with fewer seeds per tree per year than are needed for a traditional parentage study.