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Because the water status of grapevines strongly affects the quality of the grapes and resulting wine, automated and early drought stress detection is important. Plant measurements are very promising for detecting drought stress, but strongly depend on microclimatic changes. Therefore, conventional stress detection methods require threshold values which define when plants start sensing drought stress. There is however no unique method to define these values. In this study, we propose two techniques that overcome this limitation. Two statistical methods were used to automatically distinguish between drought and microclimate effects, based on a short preceding full-irrigated period to extract plant behaviour under normal conditions: Unfold Principal Component Analysis (UPCA) and Functional Unfold Principal Component Analysis (FUPCA). Both techniques aimed at detecting when measured sap flow rate or stem diameter variations in grapevine deviated from their normal behaviour due to drought stress. The models based on sap flow rate had some difficulties to detect stress on days with low atmospheric demands, while those based on stem diameter variations did not show this limitation, but ceased detecting stress when the stem diameter levelled off after a period of severe shrinkage. Nevertheless, stress was successfully detected with both approaches days before visible symptoms appeared. UPCA and FUPCA based on plant indicators are therefore very promising for early stress detection.

A study was conducted to elucidate the effect of N form, either NH4 + or NO3 −, on growth and solute composition of the salt-tolerant kallar grass [Leptochloa fusca (L.) Kunth] grown under 10 mM or 100 mM NaCl in hydroponics. Shoot biomass was not affected by N form, whereas NH4 + compared to NO3 − nutrition caused an almost 4-fold reduction in the root biomass at both salinity levels. Under NH4 + nutrition, salinity had no effect on the biomass yield, whereas under NO3 − nutrition, increasing salinity from 10 mM to 100 mM caused 23% and 36% reduction in the root and shoot biomass, respectively. The reduced root growth under NH4 + nutrition was not attributable to impaired shoot to root C allocation since N form did not affect the overall root sugar concentration and the starch concentration was even higher under NH4 + compared to NO3 − nutrition. The low NH4 + (≤2 mM) and generally higher amino-N concentrations in NH4 +- compared to NO3 −-fed plants indicated that the grass was able to effectively detoxify NH4 +. Salinity had no effect on Ca2+ and Mg2+ levels, whereas their concentration in shoots was lower under NH4 + compared to NO3 − nutrition (over 66% reduction in Ca2+; over 20% reduction in Mg2+), but without showing deficiency symptoms. Ammonium compared to NO3 − nutrition did not inhibit K+ uptake, and the K+-Na+ selectivity either remained unaffected or it was higher under NH4 + than under NO3 − nutrition. Results suggested that while NH4 + versus NO3 − nutrition substantially reduced root growth, and also strongly modified anion concentrations and to a minor extent concentrations of divalent cations in shoots, it did not influence salt tolerance of kallar grass.

Tree root systems, which play a major role in below-ground carbon (C) dynamics, are one of the key research areas for estimating long-term C cycling in forest ecosystems. In addition to regulating major C fluxes in the present conditions, tree root systems potentially hold numerous controls over forest responses to a changing environment. The predominant contribution of tree root systems to below-ground C dynamics has been given little emphasis in forest models. We developed the TRAP model, i.e. Tree Root Allocation of Photosynthates, to predict the partitioning of photosynthates between the fine and coarse root systems of trees among series of soil layers. TRAP simulates root system responses to soil stress factors affecting root growth. Validation data were obtained from two Belgian experimental forests, one mostly composed of beech (Fagus sylvatica L.) and the other of Scots pine (Pinus sylvestris L.). TRAP accurately predicted (R = 0.88) night-time CO2 fluxes from the beech forest for a 3-year period. Total fine root biomass of beech was predicted within 6% of measured values, and simulation of fine root distribution among soil layers was accurate. Our simulations suggest that increased soil resistance to root penetration due to reduced soil water content during summer droughts is the major mechanism affecting the distribution of root growth among soil layers of temperate Belgian forests. The simulated annual rate of C input to soil litter due to the fine root turnover of the Scots pine was 207 g C m−2 yr−1. The TRAP model predicts that fine root turnover is the single most important source of C to the temperate forest soils of Belgium.

The paper presents the results of amino acid analyses in xylem sap during leaf regrowth of ryegrass plants defoliated firstly at the 8th and secondly at the 12th week of culture. The free amino acid composition of leaves, stubble and roots was also determined and some of the results are reported. Prior to defoliation, xylem sap contained a high proportion of amides, particularly glutamine. During regrowth after defoliation, the proportion of asparagine in the xylem sap increased until the third day when the highest ratios of asparagine/glutamine appeared. The results are compared with relative amounts of free amino acids in the different plant parts and discussed in relation to source-sink nitrogen transfer.

A 2D physically based framework is proposed to analyze the effect of a non-uniform water supply at the soil surface generated by rainfall interception and stemflow on soil-root water transport in the case of heterogeneous distribution of the roots in the soil profile. To model soil-root water transport, the root water potential of two plants placed in two adjacent rows was simulated so as to minimize the difference between the evaporative demand and the amount of water taken up by each plant. A characterization of the throughfall to incident rainfall, soil hydrodynamic properties, soil-root contacts, and maize evapotranspiration, was carried out during a 10-day experiment with a leaf area index of about 4 to 5 m2 m−2. Mean rainfall interception percentages were in the [47.4%–52.6%] range at half the distance between two adjacent rows, whereas an interception percentage higher than 80% was found near the stems along the rows. As a result, the mean estimated stemflow was 1 L per plant per 16.4 mm water supply above the canopy. Good agreement was found between the measured and predicted transpiration values. As the soil started to moisten, the predicted root water potential rapidly increased, in line with the predicted number of active roots that rapidly decreased. Effects due to stemflow during infiltration disappeared progressively when drying was in progress. The proposed approach could be useful for analyzing soil-root water transport and possible pollution when solutes move with water under various realistic conditions where non-uniform water supply is involved.

Limitations to agricultural productivity imposed by the root-zone constraints in Australian dryland soils are severe and need redemption to improve the yields of grain crops and thereby meet world demand. Physical, chemical and biological constraints in soil horizons impose a stress on the plant and restrict plant growth and development. Hardsetting, crusting, compaction, salinity, sodicity, acidity, alkalinity, nutrient deficiencies and toxicities due to boron, carbonates and aluminium are the major factors that cause these constraints. Further, subsoils in agricultural regions in Australia have very low organic matter and biological activity. Dryland salinity is currently given wide attention in the public debate and government policies in Australia, but they only focus on salinity induced by shallow groundwater. However, the occurrence of transient salinity in root-zone layers in the regions where water tables are deep is an important issue with potential for larger economic loss than water table-induced seepage salinity. Root-zone constraints pose a challenge for salinity mitigation in recharge as well as discharge zones. In recharge zones, reduced water movement in sodic horizons results in salt accumulation in the root zone resulting in chemical and physical constraints that reduce transpiration that, in turn, upsets salt balance and plant growth. High salinity in soil and groundwater restricts the ability of plants to reduce water table in discharge zones. Thus plant-based strategies must address different kinds of limitations in soil profiles, both in recharge and discharge zones. In this paper we give an overview of plant response to root-zone constraints but with an emphasis on the processes of salt accumulation in the root-zone of soils. We also examine physical and chemical methods to overcome subsoil limitations, the ability of plants to adapt to and ameliorate these constraints, soil modification by management of agricultural and forestry ecosystems, the use of biological activity, and plant breeding for resistance to the soil constraints. We emphasise that soil scientists in cooperation with agronomists and plant breeders should design site-specific strategies to overcome multiple soil constraints, with vertical and lateral variations, and to develop plant-based solutions for dryland salinity.