Linkages between traits and decomposition of weed communities along a soil management and pedoclimate gradient in Mediterranean vineyards.

BACKGROUND AND AIMS: Decomposition is a major ecosystem process which improves soil quality. Despite that, only a few studies have analysed decomposition in an agricultural context, while most agrosystems (e.g. vineyards) are facing decreasing soil quality. The objective of this study is to understand the impacts of both pedoclimate and weed management on the mass loss of vineyard weed communities during the early stages of the decomposition process through their functional properties. METHODS: In 16 Mediterranean vineyards representing both a pedoclimate and a soil management gradient, we measured the mass loss of green above-ground biomass of 50 weed communities during decomposition in standard conditions and key leaf traits of dominant species [e.g. leaf dry matter content (LDMC) and leaf lignin to nitrogen ratio (lignin:N)]. Both the mean [i.e. community-weighted mean (CWM)] and diversity (i.e. Rao index) were computed at the community level. Path analysis was used to quantify the effects of agro-environmental filters on the mass loss of weed communities through their functional properties. KEY RESULTS: Tillage and mowing filtered more decomposable communities than chemical weeding (16 and 8 % of higher mass loss after 2 months of decomposition). Path analysis selected weed management practice type as the main factor determining mass loss through its effect on functional properties, while soil and climate had minor and no effects, respectively. Chemical weeding favoured communities with higher investment in resistant leaves (e.g. 38 % higher lignin:N, 22 % lower leaf nitrogen content) which resulted in lower mass loss compared with tilled and mowed communities. Mowing favoured communities with 47 % higher biomass and with 46 % higher nitrogen content. CONCLUSIONS: Weed management significantly influenced weed mass loss, while the pedoclimate had little effect. Our results suggest that mowing is a promising alternative to herbicide use, favouring higher biomass, nitrogen content and decomposability potential of weeds.

Quantification of the pluriannual dynamics of grapevine growth responses to nitrogen supply using a Bayesian approach.

The effect of nitrogen (N) nutrition on grapevine carbon (C) dynamics has been well studied at the annual scale, but poorly addressed at a pluriannual timescale. The aim of this study was to quantify, in an integrated conceptual framework, the effect of N nutrition on potted grapevine growth and storage over 2 consecutive years. The consequences of using destructive measurements were investigated using a hierarchical Bayesian model. The rate and duration of leaf growth were both positively impacted by the chlorophyll content of the leaves, but they were negatively impacted by the initial carbohydrate measurements, raising a distortion in the estimation of initial reserves. The C production per unit of global radiation depended on the leaf area dynamics. The allocation of dry matter mainly relied on the phenological stage. The present study highlights the importance of using appropriate statistical methods to overcome uncertainties due to destructive measurements. The genericity of the statistical approach presented may encourage its implementation in other agronomy studies. Based on our results, a simple conceptual framework of grapevine pluriannual growth under various N supplies was built. This provides a relevant basis for a future model of C and N balance and responses to N fertilization in grapevine.

Nitrogen supply controls vegetative growth, biomass and nitrogen allocation for grapevine (cv. Shiraz) grown in pots.

Maintaining grapevine productivity with limited inputs is crucial in Mediterranean areas. Apart from water, nitrogen (N) is also an important limiting factor in grape growing. The effects of N deficiency on grapevine growth were investigated in this study. Two-year-old Vitis vinifera L.cv. Shiraz plants grafted on 110 R were grown in pots placed outside and exposed to various N supplies (0, 0.6, 1.2, 2.4 and 12g plant-1) under well-watered conditions. At veraison, plants were harvested and organs separately dried, weighed and analysed for N. During plant growth, the length of the primary and secondary axes and the number of leaves on them were recorded. The N content of leaves was also analysed at three phenological stages (flowering, bunch closure and veraison). All growth processes were inhibited by N deficiency in an intensity-dependent manner. Quantitative relationships with N supply were established. Vegetative growth responded negatively to N stress when comparing control N supply with no N supply: primary axis elongation (-61%), leaf emergence on the primary axis (-47%), leaf emergence on the secondary axis (-94%) and lamina area expansion (-45%). Significant differences on the plant N status were observed from flowering onwards which might be useful for managing fertilisation.