webservice传参问题

版本为.net 8.2
通过webservice启动流程，如何传入日期类型参数？

ServiceReference1.BPMServiceSoapClient client = new ServiceReference1.BPMServiceSoapClient();
List<ServiceReference1.DataItem> dataItems = new List<ServiceReference1.DataItem>();
//ItemName 数据项名称，ItemValue为object类型，会自动识别处理，直接赋值即可
dataItems.Add(new ServiceReference1.DataItem() { ItemName = "提交时间", ItemValue = DateTime.Now });
var result= client.StartWorkflow("Test", "Test", "administrator", "WebService发起", true, dataItems.ToArray());