Soil available phosphorus (AP) deficiency and shortage of phosphate rocks limit cotton production in China. Therefore, pool-culture experiments were conducted in 2019 and 2020 using two cotton cultivars (CCRI-79, low-P tolerant; SCRC-28, low-P sensitive) under three soil AP levels (P₀: 3 ± 0.5, P₁: 6 ± 0.5, and P₂ (control): 15 ± 0.5 mg kg⁻¹) to ascertain the effect of soil AP on boll biomass and lint yield. P₀ and P₁ decreased the P concentration and net photosynthetic rate (Pn) of subtending leaves, thus, reducing boll biomass and lint yield. Additionally, soil AP deficiency decreased boll wall:boll, lint:boll, and lint:seed, and increased seed:boll ratio. Upper fruiting branch positions (FB_9–12) had higher lint:seed ratio and proportion of the total lint yield under low soil AP. Moreover, soil AP deficiency also reduced the sucrose transformation rate (Tr) and activities of sucrose-metabolizing enzymes, such as ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), sucrose phosphate synthase (SPS), and sucrose synthase (SuSy), while increased carbohydrate levels (soluble sugar, sucrose, and starch) and the activity of cytosolic fructose-1,6-bisphosphatase (cy-FBPase) in the subtending leaves. The sucrose and starch contents, cy-FBPase, and SPS activities of SCRC-28 were more sensitive to low soil AP than CCRI-79. Higher Tr and activities of initial Rubisco and SuSy in the subtending leaves improved boll biomass and lint yield.

Introduction: Phosphorus (P) deficiency hinders cotton (Gossypium hirustum L.) growth and development, seriously affecting lint yield and fiber quality. However, it is still unclear how P fertilizer affects fiber length.Methods: Therefore, a two-year (2019-2020) pool-culture experiment was conducted using the split-plot design, with two cotton cultivars (CCRI-79; low-P tolerant and SCRC-28; low-P sensitive) as the main plot. Three soil available phosphorus (AP) contents (P₀: 3 ± 0.5, P₁: 6 ± 0.5, and P₂ (control) with 15 ± 0.5 mg kg⁻¹) were applied to the plots, as the subplot, to investigate the impact of soil AP content on cotton fiber elongation and length. Results: Low soil AP (P₀ and P₁) decreased the contents of the osmotically active solutes in the cotton fibers, including potassium ions (K⁺), malate, soluble sugar, and sucrose, by 2.2–10.2%, 14.4–47.3%, 8.7–24.5%, and 10.1–23.4%, respectively, inhibiting the vacuoles from facilitating fiber elongation through osmoregulation. Moreover, soil AP deficiency also reduced the activities of enzymes participated in fiber elongation (plasma membrane H⁺-ATPase (PM-H⁺-ATPase), vacuole membrane H⁺-ATPase (V-H⁺-ATPase), vacuole membrane H⁺-translocating inorganic pyrophosphatase (V-H⁺-PPase), and phosphoenolpyruvate carboxylase (PEPC)). The PM-H⁺-ATPase, V-H⁺-ATPase, V-H⁺-PPase, and PEPC were reduced by 8.4–33.0%, 7.0–33.8%, 14.1–38.4%, and 16.9–40.2%, respectively, inhibiting the transmembrane transport of the osmotically active solutes and acidified conditions for fiber cell wall, thus limiting the fiber elongation. Similarly, soil AP deficiency reduced the fiber length by 0.6–3.0 mm, mainly due to the 3.8–16.3% reduction of the maximum velocity of fiber elongation (V_Lmax). Additionally, the upper fruiting branch positions (FB_10–11) had higher V_Lmax and longer fiber lengths under low soil AP. Discussion: Cotton fibers with higher malate content and V-H⁺-ATPase and V-H⁺-PPase activities yielded longer fibers. And the malate and soluble sugar contents and V-H⁺-ATPase and PEPC activities in the SCRC-28's fiber were more sensitive to soil AP deficiency in contrast to those of CCRI-79, possibly explaining the SCRC-28 fiber length sensitivity to low soil AP.

Long-termrotary tillage has led to a deterioration in cotton production. It remains unclear whether soil inversion with subsoiling could halt the deterioration. Here, a field experiment was set from 2015 to 2017 with three treatments: CK, 15 cm rotary tillage; T1, replace the top 20 cm soil layer with the 20–40 cm soil layer and loosen the 40–55 cm soil layer; T2, replace the top 20 cm soil layer with the 20–40 cm soil layer and loosen the 40–70 cm soil layer. The results showed that the total nitrogen(N) content, alkaline N content, total phosphorous(P) content, available P content, and available potassium(K) content of T1 and T2 in the 20–40 cm soil layer were significantly higher than those in the top 20 cm soil layer in 2017, and the soil nutrient contents in the top 20 cm soil layer increased with each planting season. Compared with CK, the root dry matter of T1 and T2 increased by 13.1% and 15.2%, respectively, and the boll number and boll weight were also significantly higher, and the seed cotton yield under T1 for the three years increased by 7.7%, 7.6%, and 6.1%, respectively, and the seed cotton yield under T2 for the three years increased by 6.1%, 8.6%, and 8.2%, respectively. The results suggest that soil inversion with subsoiling is a continuously effective tillage practice for increasing the output of cotton in the North China Plain.

Background: Soil available phosphorus (AP) deficiency significantly limits cotton production, particularly in arid and saline-alkaline regions. Screening cotton cultivars for low phosphorus (P) tolerance is crucial for the sustainable development of cotton production. However, the effect of different growth media on the screening outcomes remains unclear. To address this, we evaluated the low P tolerance of 25 cotton cultivars through hydroponic culture at two P levels (0.01 and 0.5 mmol•L⁻¹ KH₂PO₄) in 2018 and field culture with two P rates (0 and 90 kg•hm⁻², in P₂O₅) in 2019. Results: In the hydroponic experiments, principal component analysis (PCA) showed that shoot dry weight (SDW) and P utilization efficiency in shoots (PUES) of cotton seedlings explained over 45% of the genetic variation in P nutrition. Cotton cultivars were subjected to comprehensive cluster analysis, utilizing agronomic traits (SDW and PUES) during the seedling stage (hydroponic) and yield and fiber quality traits during the mature stage (in field). These cultivars were grouped into four clusters: resistant, moderately resistant, moderately sensitive, and sensitive. In low P conditions (0.01 mmol•L⁻¹ KH₂PO₄ and 4.5 mg•kg⁻¹ AP), the low-P-resistant cluster showed significantly smaller reductions in SDW (54%), seed cotton yield (3%), lint yield (− 2%), fiber length (− 1%), and fiber strength (− 3%) compared with the low-P-sensitive cluster (75%, 13%, 17%, 7%, and 9%, respectively). The increase in PUES (299%) in the resistant cluster was also significantly higher than in the sensitive cluster (131%). Four of the eight low-P-tolerant cotton cultivars identified in the field and six in the hydroponic screening overlapped in both screenings. Two cultivars overlapped in both screening in the low-P-sensitive cluster. Conclusion: Based on the screenings from both field and hydroponic cultures, ZM-9131, CCRI-79, JM-958, and J-228 were identified as low-P-tolerant cotton cultivars, while JM-169, XM-33B, SCRC-28, and LNM-18 were identified as low-P-sensitive cotton cultivars. The relationship between field and hydroponic screening results for low-P-tolerant cotton cultivars was strong, although field validation is still required. The low P tolerance of these cultivars was closely associated with SDW and PUES.