Effects on the root morphology and mircostructure of young pear (Pyrus pyrifolia) tree by split-root supply of bioorganic and chemical fertilizer

Bioorganic fertilizers are widely used in fruit orchards to improve soil properties and increase productivity. To investigate the effects of bioorganic fertilizer (BIO) and chemical fertilizer (CF) on the root system architecture and above-ground growth of pear trees, a split-root experiment was conducted. To this end, six soil amendment combinations were investigated: NF–NF (no fertilizer), NF-CF, NF-BIO, CF-CF, BIO-BIO, and BIO-CF. Roots of 1-year old ‘Cuiguan’ pear trees were distributed as evenly as possible into split-root chambers containing the aforementioned amendment combinations and maintained for 210 days after budding. Results showed that in boxes containing the same fertilizer in both chambers (NF–NF, CF-CF and BIO-BIO), the BIO chambers had an improved soil pH, by 0.6–0.8 units, and 23%–65.5% greater SOM than the soils in the NF and CF chambers. We also found that in these BIO chambers the lateral root number was 2.1–3.5 times greater than in NF and CF chambers and the maximum order of lateral roots was greater than 9. BIO application promoted lateral root growth in the paired NF and CF chambers, increasing specific root length and reducing root tissue density. In BIO-CF boxes, the 4th to 6th lateral root number and length accounted for the largest proportion of total lateral root number and length respectively. Moreover, compared with trees grown in CF-CF, those grown in BIO-BIO and BIO-CF had greater mean xylem, phloem, and cork layer thicknesses, as well as greater mean vessel density and number. BIO-CF treated soils had significantly reduced (50%) available phosphorus content compared to CF-CF treated soils, and consistently, BIO-CF resulted in the greatest growth of trunk girth (by 5–29%) among all the treatments. Soil organic matter and nitrate nitrogen concentration had significantly positive effects on root growth and activity, while branching intensity was significantly related to available phosphorus content and total nitrogen, followed by available potassium content and ammonia nitrogen content. In conclusion, local application of bioorganic fertilizer is a promising technique to sustainably maintain pear tree productivity because it accelerates the root proliferation and activity in either nutrient-deficient or -sufficient soil.