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Root foraging of birch and larch in heterogeneous soil nutrient patches under water deficit.

ABSTRACT: Water and nutrient are two critical factors that limit plant growth to spatial-temporal extents. Tree root foraging behavior has not received adequate attention in heterogeneous soil environments in temperate forest under drought pressure. In this study, birch (Betula platyphylla) and larch (Larix olgensis) seedlings were raised in pots in a split-root system with artificially heterogeneous soil environments to study the root foraging response to drought. Potted space was split into two halves where substrates were mixed with fertilizers in 67.5 mg nitrogen (N) plant-1 (N-P2O5-K2O, 14-13-13) to both halves as to create a homogeneous condition. Otherwise, a rate of 135 mg N plant-1 of fertilizers was delivered to a random half to create a heterogeneous condition. Half of seedlings were fully sub-irrigated every three days with the other half received the drought treatment by being watered every six days. Both birch and larch seedlings showed greater net shoot growth and biomass increment in well-watered condition, while root morphology was promoted by drought. Both species placed more fine roots with higher root N concentration in nutrient-enriched patches. In the heterogeneous pattern, birch showed a higher foraging precision assessed by biomass and greater foraging plasticity assessed in morphology and physiology. In contrast, larch seedlings had higher root N concentration in the well-watered condition. Neither species showed a significant response of N utilization to the heterogeneous pattern, but both used more N when water supply was improved. Overall, birch is better at acclimating to heterogeneous soil conditions, but its ability to seize N was lower than larch when drought was alleviated.

SUBMITTER: Tan L

PROVIDER: S-EPMC8354452 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Drought is a serious problem that causes losses in crop-yield every year, but the mechanisms underlying how roots respond to water deficit are difficult to study under controlled conditions. Methods for assaying root elongation and architecture, especially for seedlings, are commonly achieved on artificial media, such as agar, moistened filter paper, or in hydroponic systems. However, it has been demonstrated that measuring root characteristics under such conditions does not accurately mimic what is observed when plants are grown in soil. Morphological changes in root behavior occur because of differences in solute diffusion, mechanical impedance, exposure to light (in some designs), and gas exchange of roots grown under these conditions. To address such deficiencies, we developed a quantitative method for assaying seedling root lengths and germination in soil using a plate-based approach with wheat as a model crop. We also further developed the method to include defined water deficits stress levels using the osmotic properties of polyethylene glycol (PEG). Seeds were sown into soil-filled vertical plates and grown in the dark. Root length measurements were collected using digital photography through the transparent lid under green lighting to avoid effects of white light exposure on growth. Photographs were analyzed using the cross-platform ImageJ plugin, SmartRoot, which can detect root edges and partially automate root detection for extraction of lengths. This allowed for quick measurements and straightforward and accurate assessments of non-linear roots. Other measurements, such as root width or angle, can also be collected by this method. An R function was developed to collect exported root length data, process and reformat the data, and output plots depicting root/shoot growth dynamics. For water deficit experiments, seedlings were transplanted side-by-side into well-watered plates and plates containing PEG solutions to simulate precise water deficits.

Project description:Typical small-pot culture systems are not ideal for controlled environment phenotyping for drought tolerance, especially for root-related traits. We grew soybean plants in a greenhouse in 1-m rooting columns filled with amended field soil to test the effects of drought stress on water use, root growth, shoot growth, and yield components. There were three watering treatments, beginning at first flower: watered daily to 100% of the maximum soil water holding capacity (control), 75% (mild drought stress), or 50% (drought stress). We also tested whether applying fertilizer throughout the 1-m soil depth instead of only in the top 30 cm would modify root distribution by depth in the soil profile and thereby affect responses to drought stress. Distributing the fertilizer over the entire 1-m soil depth altered the root biomass distribution and volumetric soil water content profile at first flower, but these effects did not persist to maturity and thus did not enhance drought tolerance. Compared to the control (100%) watering treatment, the 50% watering treatment significantly reduced seed yield by 40%, pod number by 42%, seeds per pod by 3%, shoot dry matter by 48%, root dry matter by 53%, and water use by 52%. Effects of the 75% watering treatment were intermittent between the 50 and 100%. The 50% treatment significantly increased root-to-shoot dry matter ratio by 23%, harvest index by 17%, and water-use efficiency by 7%. Seed size was not affected by either fertilizer or watering treatments. More than 65% of the total root dry matter was distributed in the upper 20 cm of the profile in all watering treatments. However, the two drought stress treatments, especially the mild drought stress, had a greater proportion of root dry matter located in the deeper soil layers. The overall coefficient of variation for seed yield was low at 5.3%, suggesting good repeatability of the treatments. Drought stress imposed in this culture system affected yield components similarly to what is observed in the field, with pod number being the component most strongly affected. This system should be useful for identifying variation among soybean lines for a wide variety of traits related to drought tolerance.

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Root foraging of birch and larch in heterogeneous soil nutrient patches under water deficit.

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