# Biochar Improved Sugarcane Growth and Physiology under Salinity Stress
## 1 Introduction  
Salinity stress is one of the major determinants leading to the loss of crop productivity worldwide [1]. With the increase in both frequency and intensity of agricultural land salinization caused by climate change and poor land management [2], the effects of soil salinity are becoming more critical. Of note, almost 20% of the world's cultivated land is affected by salt stress [3], and the salt-affected soils were extensively found in arid and semi-arid regions [4]. Salinity negatively affects physiological and biochemical processes in plants as it triggers osmotic stress and ion toxicity [5]. Additionally, this condition also accelerates the generation of reactive oxygen species (ROS) leading to oxidative damage in cellular components and, thus, severely interrupting plant cell functions. Salt stressdecreases crop dry matter yield, chlorophyll content, and gas exchange variables [6,7]. Furthermore, [PERSON] et al. [8] reported that photosynthetic activity decreased in sorghum growing under saline conditions, owing to a conspicuous decline in plant growth and productivity. High severity and long duration of salt stress cause significant yield loss or even plant death [9]. As the effects of salinity are adverse and increasing, sustainable strategies and proper techniques for mitigating its impacts are critically important. As a glycopyle plant, sugarcane's growth is adversely inhibited by soil salinity [10,11]. Sugarcane is moderately sensitive to salinity stress as indicated by the decrease in stem diameter, stalk population, leaf area, and dry matter accumulation. [PERSON] et al. [12] also noted that plant height and node number of sugarcane plants were sensitive to soil salinity. [PERSON] et al. [13] observed root length, shoot, and root fresh weight decreased by salinity, and the damage symptoms were more pronounced at salt levels above 100 mM. [PERSON] et al. [14] reported that the growth and physiological parameters of sugarcane were inhibited by increasing salt concentration in irrigation water. Climate change with the rising of salimization constrains sugarcane production in coastal lands in Southeast Asia, Taiwan, Japan islands, the Amazon basin, etc. [PERSON] and [PERSON] [15] reported the same status in Australia and South Florida (USA). Biochar is a carbon-rich product obtained from the pyrolysis of charred organic materials under high temperatures and oxygen-deficient conditions [16]. Therefore, the properties of biochar mainly depend on the pyrolysis temperature and pyrolyzed matrix. High pyrolysis temperature promotes the biochars with strongly developed specific surface area, high porosity, pH, ash, and carbon contents, but with low cation exchange capacity (CEC) and volatile matter [17]. In addition, the quality of biochar is highly influenced by the type of feedstocks [18]. Until now, two common types of feedstocks for biochar were plant residue and manure sources [19]. While plant-derived (crop residue and wood biomass) biochars exhibited higher surface areas, carbon content, and volatile matter, manure-derived biochars produced higher CEC even at higher pyrolysis temperatures [17]. The potential of utilizing biochar to improve soil health has received considerable attention in recent years [4]. Application of biochar enriches soil physicochemical properties, biological properties, and soil enzymatic activity, hence contributing to a favorable plant-soil interaction platform. Several studies have revealed that biochar application may substantially improve soil fertility and crop productivity. As a direct mechanism, biochar acts to reduce sodium uptake by plants as it retains the sodium amount (transient binding of Na+), reduces the osmotic stress by maintaining soil moisture content, and releases mineral nutrients (particularly K+, Ca++, Mg++) into the soil environment [20,21]. Additionally, biochar greatly increased the water-holding capacity of the soil, therefore enhancing leaf chlorophyll content, stomatal conductance, photosynthetic rate, and relative water content [22,23].