Species-Specific Responses of Root Morphology of Three Co-existing Tree Species to Nutrient Patches Reflect Their Root Foraging Strategies

Root foraging strategies of plants may be critical to the competition for nutrient resources in the nutrient patches, but little is known about these of co-existing tree species in subtropical regions. This study aimed to elucidate root foraging strategies of three co-existing tree species in nutrient heterogeneous soils by exploring their root distribution, root morphology, photosynthates allocation and nutrient accumulation. Seedlings of the three tree species [moso bamboo (Phyllostachys edulis), Chinese fir (Cunninghamia lanceolata), and masson pine (Pinus massoniana)] were grown for 8months under one homogeneous soil [uniform nitrogen (N) plus phosphorus (P)] and three heterogeneous soils (localized N supply, localized P supply, or localized N plus P supply). The biomass, root morphological parameters (i.e., root length and root surface area), specific root length (SRL), non-structural carbohydrates (NSCs, i.e., mobile sugar and starch) in roots, total N and total P of plants were measured. The plasticity and distribution of root system were analyzed by calculating the root response ratio (RRR) and root foraging precision (FP), respectively. The results are as follows (i) Chinese fir tended to forage more N by promoting root proliferation in the N-rich patch, while root proliferation of bamboo and pine did not change. For P, bamboo absorbed more P by promoting root proliferation in the P-rich patch. The total P content of Pine and Chinese fir under localized P supply treatment remain the same despite the fact that the root length in the P-rich patch and the FP increased. (ii) Chinese fir foraged more N by increasing root length and decreasing SRL in the NP-rich patch; bamboo foraged more N and P by increasing root length and SRL in the NP-rich patch. The FP and foraging scale (FS) of both bamboo and Chinese fir were significantly improved under localized N plus P treatment. (iii) The concentrations of NSC were positively correlated with root morphological plasticity for moso bamboo and Chinese fir. Our results indicated that higher morphological plasticity is exhibited in moso bamboo and Chinese fir than masson pine in nutrient heterogeneous soils, allowing them to successfully forage for more nutrients.

Considerations for Selecting Potassium Placement Methods in Soil

Placement strategies can be a key determinant of efficient use of applied fertilizer potassium (K), given the relative immobility of K in all except the lightest textured soils or high rainfall environments. Limitations to K accessibility by plants caused by immobility in the soil are further compounded by the general lack of K-stimulated root proliferation in localized soil zones enriched with K alone, compared with root proliferation due to concentrated N and P. Further, effects of K fixation reactions in soils with certain clay mineralogies and the declining concentration and activity of soil solution K with increasing clay content can also limit plant K acquisition. Variation in root system characteristics among crops in a rotation sequence and fluctuating soil moisture conditions in fertilized soil horizons in rain-fed systems increase the complexity of fertilizer placement decisions to ensure efficient K recovery and use. This complexity has resulted in extensive exploration of fertilizer K application strategies, with this chapter focusing on K applications to the soil. Issues discussed include comparisons of broadcast versus banded applications, depth of fertilizer placement, and the impacts of co-location of K with other nutrients. While research findings are often specific to the crop, soil, and seasonal conditions under which they are conducted, we attempt to identify strategies that most consistently deliver improved crop recovery and utilization of fertilizer K.

Effect of rhizospheric nutrient management on root growth, yield, and nutrient use efficiency of wheat (Triticum aestivum L.) under Tarai region of Uttarakhand, India

Rhizospheric nutrient management and fertilizer placement can be a useful measure to improve wheat crops productivity in Tarai regions of India. An experiment was conducted to evaluate the effects of rhizospheric nutrient management on wheat (Triticum aestivum L.) to explore the relationship between root proliferation, grain yield and NUE in Tarai region of Uttarakhand, India. It comprised 3 fertilizer application (P1 to P3) and 6 nutrient management treatments (T1 to T6) with absolute control in a randomized complete block design and replicated thrice. Experimental results indicated that P1 (1.29 and 1.47; 1.84 and 2.29 mg/cc) produced greater root density, and compared to P3 (1.39 and 1.49; 1.74 and 2.17 mg/cc), P2 (1.24 and 1.36; 1.68 and 1.97 mg/cc) and absolute control (0.85 and 1.19; 1.42 and 1.69 mg/cc) at maximum tillering and flowering stage in year 2017-18 and 2018-19, respectively .The root proliferation also influenced the grain yield (5.4 and 5.5; 5.3 and 5.3; 5.1 and 5.2; 3.5 and 3.3 t/ha ) in P1, P3, P2 and absolute control in the year 2017-18 and 2018-19, respectively. However, the grain yield and root distributions (at the flowering stage) recorded significantly (p=0.05) maximum in T4 (5.8 and 5.7 t/ha; 1.84 and 2.32 mg/cc) followed by T3, T6, T1, T5, T2 treatments and minimum in absolute control (3.5 and3.3 t/ha; 1.42 and 1.69 mg /cc) in the year of 2017-18 and 2018-19, respectively. Thus, the rhizospheric nutrient management (75% RDF+ vermicompost + PSB) with fertilizer placement can be a feasible approach for increasing grain yield and NUE in Tarai regions of Uttarakhand, by promoting deep root development and reducing fertilizer inputs in wheat.

Bioavailability and -accessibility of subsoil allocated 33P-labelled hydroxyapatite to wheat under different moisture supply

Information on the bioavailability and -accessibility of subsoil phosphorus (P) and how soil moisture affects its utilization by plants is scarce. The current study examined whether and to which degree wheat acquires P from subsoil allocated hydroxyapatite and how this could be affected by soil moisture. We investigated the 33P uptake by growing wheat in two rhizotron trials (soil and sand) with integrated 33P-labelled hydroxyapatite hotspots over a period of 44 days using digital autoradiography imaging and liquid scintillation counting. We applied two irrigation scenarios, mimicking either rainfall via topsoil watering or subsoil water storage. The plants showed similar biomass development when grown in soil, but a reduced growth in sand rhizotrons. Total plant P(tot) stocks were significantly larger in plants grown under improved subsoil moisture supply, further evidenced by enhanced P stocks in the ears of wheat in the sand treatment due to an earlier grain filling. This P uptake is accompanied by larger 33P signals, indicating that the plants accessed the hydroxyapatite because subsoil irrigation also promoted root proliferation within and around the hotspots. We conclude that even within a single season plants access subsoil mineral P sources, and this process is influenced by water management.