Carbon allocation to the root system of tropical tree Ceiba pentandra using 13C pulse labelling in an aeroponic facility

Effects of drought and nutrient deficiencies on the allocation of recently fixed carbon in a plant-soil-microbe system

Carbon (C) allocation plays an important role in plant adaptation to water and nutrient stresses. However, the effects of drought and nutrient deficiencies on the allocation of recently fixed C in the plant-soil-microbe system remain largely unknown. Herein, we studied the response of C allocation of Sophora moorcroftiana (an indigenous pioneer shrub in Tibet) to drought, nitrogen (N) deficiency and phosphorus (P) deficiency using a microcosm experiment. The 13CO2 continuous labeling was used to trace C allocation in the plant-soil-microbe system. We found that drought significantly reduced plant 13C, but it increased 13C accumulation in soil. The decreased plant 13C under drought was attributed to the decrease of 13C in stem and root rather than that in leaf. The excess 13C fraction in the microbial biomass (MB13C) was reduced by N deficiency, but it was not affected by the combination of drought and N deficiency, indicating that drought weakened the effects of N deficiency on MB13C. By contrast, MB13C increased under the combination of drought and P deficiency, suggesting that drought enhanced the effects of P deficiency on MB13C. Drought and nutrient deficiencies regulated the belowground 13C allocation. Specifically, drought and P deficiency increased the allocation of 13C to root and N deficiency regulated the allocation of 13C to microbial biomass C and dissolved organic C in soil. Notably, soil 13C decreased with increasing plant 13C, while MB13C first decreased and then increased with increasing plant 13C. Overall, our study demonstrated that drought and nutrient deficiencies interactively affected C allocation in a plant-soil-microbe system and provided insights into C allocation strategies in response to multiple resource (water and nutrient) stresses under environmental changes.

Patterns of total root and shoot carbon dioxide fluxes and their impact on daily tree carbon budget in large tropical tree saplings

A significant amount of the carbon (C) assimilated in photosynthesis by trees is re-emitted to the atmosphere via the respiratory CO2 flux of roots. Because of technical constraints, we have little understanding of the extent and dynamics of the respiratory CO2 flux of roots at the total root system scale (RCF). This study aimed to fill this gap and to quantify the daily C budget of entire trees. We used aeroponics as a novel approach to measure directly and simultaneously RCF and the net CO2 flux of the entire shoot (SCF), to estimate their night- and day-time contributions to daily tree CO2 budget and to estimate the relative contribution of different root categories to RCF in large saplings of the tropical tree species Ceiba pentandra (L.) Gaertn. By maintaining root temperature within a narrow range (24-27.5 °C), we controlled for its effect on RCF, thus allowing the potential relationship between RCF and SCF to be tested. The carbon gain of the fast-growing saplings was 0.79 ± 0.10 g C sapling-1 day-1, with day-time shoot CO2 uptake outweighing night-time shoot and day- and night-time root CO2 losses by a factor of two. Other than a slight rise in the morning hours, RCF was relatively stable and not coupled to the daily dynamics of SCF. Albeit having lower specific respiration rates compared with fine-roots, the relative contributions of coarse-roots (diameter >2 mm) to RCF were substantial because of their large biomass and were estimated to range from 43 to 63% of RCF at midday of different days during the growing season. The results of this study suggest that (i) the entire root system needs to be monitored for its impact on the tree CO2 budget, (ii) RCF cannot be derived from SCF and (iii) the importance of coarse-root respiration to RCF may be greater than appreciated.

Sustainable Production of Insecticidal Compounds from Persea indica

In this work, we have investigated the accumulation of ryanoids in different plant parts (leaves, stems and roots) of aeroponically grown Persea indica cloned trees (one-year-old cloned individuals) and a selected mature, wild tree. We tested the insect antifeedant (against Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi) and nematicidal (against Meloidogyne javanica) effects of ethanolic extracts from these different plant parts. The HPLC-MS analysis of P. indica extracts showed that mature tree (wild) leaves had two times more chemical diversity than stems. Aeroponic plants showed fewer differences in chemical diversity between leaves and stems, with the lowest diversity found in the roots. Ryanodane epiryanodol (1) was present in all the plant parts, with the mature stems (wild) containing the highest amount. The aeroponic stems also accumulated ryanoids including 1, cinnzeylanol (2) and cinnzeylanone (4). The insect Spodoptera littoralis was strongly affected by the stem extracts, while leaf extracts were moderately active. Based on predicted vs. real antifeedant values, we concluded that the ryanoid content (1 or a combination of 2, 4 and 1) explained the antifeedant effects of the stem extracts, while additional components contributed to the activity of the leaf extracts. Therefore, careful individual selection of P. indica seedlings should be carried out prior to proceeding with aeroponic cultivation in order to obtain ryanodane-rich stem or leaf extracts with strong antifeedant effects on S. littoralis.