The objective of this study was to determine if low stomatal conductance (g) increases growth, nitrate (NO3−) assimilation, and nitrogen (N) utilization at elevated CO2 concentration. Four Arabidopsis (Arabidopsis thaliana) near isogenic lines (NILs) differing in g were grown at ambient and elevated CO2 concentration under low and high NO3− supply as the sole source of N. Although g varied by 32% among NILs at elevated CO2, leaf intercellular CO2 concentration varied by only 4% and genotype had no effect on shoot NO3– concentration in any treatment. Low-gNILs showed the greatest CO2 growth increase under N limitation but had the lowest CO2 growth enhancement under N-sufficient conditions. NILs with the highest and lowest g had similar rates of shoot NO3– assimilation following N deprivation at elevated CO2 concentration. After 5 d of N deprivation, the lowest gNIL had 27% lower maximum carboxylation rate and 23% lower photosynthetic electron transport compared with the highest gNIL. These results suggest that increased growth of low-gNILs under N limitation most likely resulted from more conservative N investment in photosynthetic biochemistry rather than from low g.
ABSTRACT Root hydraulic redistribution has been shown to occur in numerous plant species under both field and laboratory conditions. To date, such water redistribution has been demonstrated in two fundamental ways, either lifting water from deep edaphic sources to dry surface soils or redistributing water downward (reverse flow) when inverted soil Ψ s gradients exist. The importance of hydraulic redistribution is not well documented in agricultural ecosystems under field conditions, and would be important because water availability can be temporally and spatially constrained. Herein we report that a North American grapevine hybrid ( Vitis riparia × V. berlandieri cv 420 A) growing in an agricultural ecosystem can redistribute water from a restricted zone of available water under a drip irrigation emitter, laterally across the high resistance pathways of the trunk and into roots and soils on the non‐irrigated side. Deuterium‐labelled water was used to demonstrate lateral movement across the vine's trunk and reverse flow into roots. Water redistribution from the zone of available water and into roots distant from the source occurred within a relatively short time frame of 36 h, although overnight deposition into rhizosphere soils around the roots was not detected. Deuterium was eventually detected in rhizosphere soils adjacent to roots on the non‐irrigated side after 7 d. Application of identical amounts of water with the same deuterium enrichment level (2%) to soils without grapevine roots showed that physical transport of water through the vapour phase could not account for either downward or transverse movement of the label. These results confirmed that root presence facilitated the transport of label into soils distant from the wetted zone. When deuterium‐labelled water was allowed to flow directly into the trunk above the root–trunk interface, reverse flow occurred and lateral movement across the trunk and into roots originating around the collar region did not encounter large disproportionate resistances. Rapid redistribution of water into the entire root system may have important implications for woody perennial cultivars growing where water availability is spatially heterogeneous. Under the predominantly dry soil conditions studied in this investigation, water redistributed into roots may extend root longevity and increase the vines water capacitance during periods of high transpiration demand. These benefits would be enhanced by diminished water loss from roots, and could be equally important to other cited benefits of hydraulic redistribution into soils such as enhancement of nutrient acquisition.
This dataset contains detailed cultivation conditions and nutrient concentrations of over 1000 samples of the edible portions of 41 cultivars of six major crop species grown between 1998-2010 across three continents at ambient and elevated atmospheric CO2 concentrations. Elevated atmospheric CO2 concentrations were achieved by free-air CO2 enrichment, which allows experimental manipulation of atmospheric composition under otherwise normal field conditions.
We investigated impacts of agricultural management practices on soil respiration (R s ) in a Cabernet Sauvignon ( Vitis vinifera ) vineyard (Oakville, CA; November 2003–December 2005). We determined (i) response of R s to cover cropping, mowing and tillage; (ii) environmental factors controlling R s ; and (iii) total annual C lost through R s A winter cover crop was either mown (CC+mow), or mown and tilled (CC+Till), and resident vegetation was tilled (RV+Till). Precipitation amount and pattern differed between years, and low R s rates occurred during summer drought and high rates during wet periods. Total CO 2 emissions differed only in Year 2 (RV+Till: 10.99 ± 0.30, CC+Till: 10.11 ± 0.49, CC+mow: 8.57 ± 0.54 Mg CO 2 –C ha −1 ). After tillage or mowing, R s increased five‐ to six‐fold in tilled treatments and two‐fold in the mown treatment (Year 1). In Year 2, R s increased two‐ to three‐fold after tillage only. R s increased after ‘post‐management’ rainfall in spring and was 1.5‐ to 2‐fold greater in tilled than mown treatments in both years due to prior incorporation of plant biomass during tillage. After fall rainfall, R s was 1.7‐fold greater in mown than tilled treatments (Year 1). Our findings suggest that the interaction of management practice with climate and soil conditions before disturbance (i.e., management and rainfall) influenced R s Polynomial regressions of R s on GWC and soil temperature indicated that R s increased until gravimetric water content (GWC) reached 14 to 15% in tilled treatments and 20% in the mown treatment, subsequently declining, indicating thresholds of GWC at which soil temperature more strongly influences R s
Extensive areas of coastal California have undergone conversion from oak woodlands or oak woodland-grassland to vineyards (Merenlender et al. 2000). Orchards or other cropping systems often preceded conversion to vineyards. Although grapevines are perennial taxa, they are more diminutive than trees, and vineyard floors are generally managed under some form of tillage. Thus, the carbon cycle has undoubtedly undergone substantial alterations as a consequence of these changes. In comparison to conversion of forest or prairie ecosystems in the Midwest, little is known about how conversion from natural to perennial agricultural ecosystems influences the carbon cycle in California’s Mediterranean climates.
Nitrogen (N) is the most limiting nutrient for plant growth and primary productivity. Inorganic N is available to plants from the soil as ammonium (NH4+) and nitrate (NO3–). We studied how wheat grown hydroponically to senescence in controlled environmental chambers is affected by N form (NH4+ vs. NO3–) and CO2 concentration ('subambient', 'ambient', and 'elevated') in terms of biomass, yield, and nutrient accumulation and partitioning. NH4+-grown wheat had the strongest response to CO2 concentration. Plants exposed to subambient and ambient CO2 concentrations typically had the greatest biomass and nutrient accumulation under both N forms. In general NH4+ plants had higher concentrations of total N, P, K, S, Ca, Zn, Fe, and Cu, while NO3– plants had higher concentrations of Mg, B, Mn, and NO3–-N. NH4+ plants contained amounts of phytate similar to NO3– plants but had higher bioavailable Zn, which could have ramifications for human health. NH4+ plants allocated more nutrients and biomass to aboveground tissues whereas NO3– plants allocated more nutrients to the roots. The two inorganic nitrogen forms influenced plant growth and nutrient status so distinctly that they should be treated separately. Moreover, plant growth and nutrient status varied in a non-linear manner with atmospheric CO2 concentration.
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