Some enzyme and respiratory activities of tropical soils from new hebrides

Activities of invertase and amylase and respiratory activities of samples of 11 soils from New Hebrides were determined. The soils mostly were under forest and were acid with medium to low C/N ratios. Invertase activities were rather low but amylase activities were similar to those found in New Zealand soils. The ratios of invertase to amylase activities were mostly low.O₂ uptakes mostly responded markedly to glucose. Most values of respiratory quotients were about 1.0. Most, but not all, dehydrogenase activities were strongly related to O₂ uptakes. On an organic C basis, these respiratory activities declined with the depths to which the soils were sampled.Biochemical activities were mostly similar in forest soils derived from basalt and from andesite. Invertase activities were lower in soils under forest than under grassland covers.All biochemical activities were correlated significantly with contents of soil moisture and organic C, less with numbers of aerobic bacteria, and negatively with soil pH. On an organic C basis, none of the biochemical activities was significantly correlated with either soil moisture content or pH.     

Root phosphatase activity of sorghum genotypes grown with organic and inorganic sources of phosphorus 1

Abstract

Relatively insoluble sources of phosphorus (P) may require solubilization, and organic P (P_o) may require hydrolysis to inorganic P (P_i) before P can be readily absorbed by plants roots. The mechanisms for these processes, however, are unknown. Root phosphatase (Pase) activity was measured to assess its relationships to P uptake by seven sorghum [Sorghum bicolor (L.) Moench] genotypes grown with P_o (ethylammonium phosphate, glycerophosphate, and phenylphosphate) and P_i (KH₂PO₄, calcium tribasic phosphate, calcium pyrophosphate, aluminum phosphate, and ferric phosphate) in nutrient solutions in a greenhouse.

Plants grown with P_o had lower root Pase activities than plants grown with P_i NB9040 and SC369–3–1JB (tolerant to low levels of P) had lower root Pase activities than CK60‐Korgi and SC33–9–8‐E4 (sensitive to low levels of P), with the other genotypes having intermediate root Pase activities. Higher root Pase activity was associated with lower root P concentrations, but Pase activity was not related to dry matter yield of roots. In experiments where genotypes were grown three weeks with KH₂PO₄ before being transferred to other sources of P, within four days root Pase activity patterns were similar to those for plants grown initially in the particular P_o or P_i compound. Root Pase activity of sorghum plants appeared to be an indicator of P status or P deficiency stress in the plants, and not associated with making P_o or P_i compounds more available for plant use.     

Norsesquiterpene glycosides in bracken ferns (Pteridium esculentum and Pteridium aquilinum subsp. wightianum) from Eastern Australia: reassessed poisoning risk to animals

Austral bracken Pteridium esculentum contains three unstable norsesquiterpene glycosides: ptaquiloside, ptesculentoside, and caudatoside, in variable proportions. The concentration of each of the glycosides was determined in this study as their respective degradation products, pterosin B, pterosin G and pterosin A, by HPLC-UV analysis. Samples of P. esculentum collected from six sites in eastern Australia contained up to 17 mg of total glycoside/g DW, with both ptaquiloside and ptesculentoside present as major components accompanied by smaller amounts of caudatoside. Ratios of ptaquiloside to ptesculentoside varied from 1:3 to 4:3, but in all Australian samples ptesculentoside was a significant component. This profile differed substantially from that of P. esculentum from New Zealand, which contained only small amounts of both ptesculentoside and caudatoside, with ptaquiloside as the dominant component. A similar profile with ptaquiloside as the dominant glycoside was obtained for Pteridium aquilinum subsp. wightianum (previously P. revolutum ) from northern Queensland and also P. aquilinum from European sources. Ptesculentoside has chemical reactivity similar to that of ptaquiloside and presumably biological activity similar to that of this potent carcinogen. The presence of this additional reactive glycoside in Australian P. esculentum implies greater toxicity for consuming animals than previously estimated from ptaquiloside content alone.     

Quantitative relationships between morphology and current soil hydrology in some Alfisols in semiarid tropical Australia

The shallow groundwater hydrology of a sequence of red, yellow, and grey earths (Paleustalfs, Plinthustalfs and Ochraqualfs of “Soil Taxonomy”) was monitored over a 9-year period (1973–1982) along a drilled transect of 30 boreholes near Torrens Creek, in northeastern Australia. Climatic analysis shows an aridic soil moisture regime under which soil water surpluses should not occur, and thus significant hydromorphism would not be expected in the soils. The present study has demonstrated, however, that profile saturation and groundwater tables may be expected to develop at various depths in the soils as often as 1 year in 3. Besides, strong linear relationships were found between a number of morphological features of the soils and various hydrological regimes currently active in the profiles: the depths to the upper limits of brown, brownish red, or red mottles, to the upper limit of ironstone gravels, and to the maximum content of clay are all most closely related to the mean position of the shallowest water tables observed; the depths to grey mottles and to mottles with chromas of two or less are most directly related to the depths at which the soils are saturated for 5 weeks; the depth to the maximum content of ironstone gravels and to the base of the solum are most closely associated with the depth at which the soils are saturated for 10 to 15 weeks; and dominantly grey colours in the strongly mottled subsols are best related to profile saturations for at least 21 weeks. The results indicate that the gley features present in the soil profiles could have developed, at least in part, in response to the current soil hydrological regime.     

Leaf-trait variation explained by the hypothesis that plants maximize their canopy carbon export over the lifespan of leaves

Measured values of four key leaf traits (leaf area per unit mass, nitrogen concentration, photosynthetic capacity, leaf lifespan) co-vary consistently within and among diverse biomes, suggesting convergent evolution across species. The same leaf traits co-vary consistently with the environmental conditions (light intensity, carbon-dioxide concentration, nitrogen supply) prevailing during leaf development. No existing theory satisfactorily explains all of these trends. Here, using a simple model of the carbon-nitrogen economy of trees, we show that global leaf-trait relationships and leaf responses to environmental conditions can be explained by the optimization hypothesis (MAXX) that plants maximize the total amount of carbon exported from their canopies over the lifespan of leaves. Incorporating MAXX into larger-scale vegetation models may improve their consistency with global leaf-trait relationships, and enhance their ability to predict how global terrestrial productivity and carbon sequestration respond to environmental change.