Niche differentiation and plasticity in soil phosphorus acquisition among co-occurring plants

How species coexist despite competing for the same resources that are in limited supply is central to our understanding of the controls on biodiversity. Resource partitioning may facilitate coexistence, as co-occurring species use different sources of the same limiting resource. In plant communities, however, direct evidence for partitioning of the commonly limiting nutrient, phosphorus (P), has remained scarce due to the challenges of quantifying P acquisition from its different chemical forms present in soil. To address this, we used 33P to directly trace P uptake from DNA, orthophosphate and calcium phosphate into monocultures and mixed communities of plants growing in grassland soil. We show that co-occurring plants acquire P from these important organic and mineral sources in different proportions, and that differences in P source use are consistent with the species’ root adaptations for P acquisition. Furthermore, the net benefit arising from niche plasticity (the gain in P uptake for a species in a mixed community compared to monoculture) correlates with species abundance in the wild, suggesting that niche plasticity for P is a driver of community structure. This evidence for P resource partitioning and niche plasticity may explain the high levels of biodiversity frequently found in P-limited ecosystems worldwide

Organic acid exudation by wild herbs in response to elevated Al concentrations

In acidic soils, monomeric aluminium (Al3+) can reach levels that are toxic to plants, thus preventing many species from growing there. Organic acids chelate Al and render it non-toxic. It has been shown that exudation of organic acids by Al-tolerant crops increases their tolerance to Al. We have extended this observation to wild plants by comparing the ability of ten herbs to exude organic acids in response to elevated Al levels. We hypothesized that exudation of organic acids was related to the ability of plants to grow on Al-rich soils. Two grasses were grown in rhizotrons in soils with 41 and 63 muM reactive Al. Organic acids were sampled from root tips connected to an intact plant-root system. Deschampsia flexuosa (L.) Trin. exuded more malic acid when grown in the soil with the highest Al content. Five forbs and five grasses were also exposed to three Al levels (0, 25 and 75 muM) in a hydroponic system. Rumex acetosella L, and Viscaria vulgaris Bernh. increased exudation of oxalic acid and Galium saxatile auct. non L. and Veronica officinalis L, increased exudation of citric acid in response to elevated Al. The distribution of the forbs in the field as described by soil pH was negatively related to the amount of organic acids exuded in response to Al. In contrast, none of the grasses exuded higher amounts of organic acids with increasing Al concentration in the hydroponic experiment. (C) 2001 Annals of Botany Company

Antiradical Properties OF Extracts From Roots, Leaves and Fruits of Six Rumex L. Species

We used the DPPH method to assess in vitro the antiradical activity of extracts from the roots, leaves and fruits of six Rumex L. (dock) species. Data from preliminary screening indicated that all the tested extracts showed antioxidant properties. The degree of antiradical activity depended upon the plant part. Fruit extracts from R. hydrolapathum Huds., R. obtusifolius L. and R. confertus Willd. showed stronger antiradical properties than the other tested material. We also determined tannin content levels in the extracts and their correlation with antioxidant activity